🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 16 (from laksa137)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa016.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://www.bbc.com/future/article/20231024-how-aliens-might-detect-our-existence-on-earth\')), getAhrefsUnparsedNoserviceFromURL(\'https://www.bbc.com/future/article/20231024-how-aliens-might-detect-our-existence-on-earth\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/www.bbc.com\/future\/article\/20231024-how-aliens-might-detect-our-existence-on-earth","crawl_time":1774377926,"first_indexed_time":1698192469,"http_code":200,"src_unparsed":"com,bbc!www,\/future\/article\/20231024-how-aliens-might-detect-our-existence-on-earth s443","src_root_hash":"1643509356818581016","history_drop_reason":null,"meta_title":"Why aliens might already know that humans exist","meta_descriptions":["Alien astronomers might be looking in our direction from distant planets. What would they see?"],"attrs_boilerpipe_text":"25 October 2023\nJonathan O'Callaghan\nFeatures correspondent\nNasa\/JSC\nThis view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa\/JSC)\nAlien astronomers might be looking in our direction from distant planets. What would they see?\nWe've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have\nidentified a few possible candidates\nfor where life might conceivably exist elsewhere in the Universe, along with the odd\nmysterious signal\n, there is yet to be any concrete evidence of alien life out there.\nThis article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, \nDoctor Who\n. \nBut what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth?\nThat's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. \"Hold the mirror up to yourself in space, and what would they see of us?\" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. \"We're looking. That means other worlds might be looking too.\"\nTo date, we have found\nmore than 5,500 planets\norbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy –\ntrillions of worlds are likely scattered throughout the Milky Way\n. Upon some of these worlds we have started to hunt both for the\nchemical signatures in their atmospheres\nthat might indicate biological activity and even\ntechnosignatures\nthat might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction.\nEarth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. \"They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers,\" he says.\nWe continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. \"Radio stations don't want to broadcast into space,\" says Thomas Beatty, an astronomer at the University of Wisconsin in the US. \"They want to broadcast to the ground.\" Other more modern forms of communication, like mobile phone signals, are\nunlikely to be detectable\n.\nNasa\/JSC\nThe light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa\/JSC)\nBut not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's\nVoyager 1 spacecraft\n, is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with.\nIn April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might\nreach other stars\nas they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. \"The signal would definitely show up as artificial,\" says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study.\nBut what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun,\nknown as a transit\n, they could see sunlight passing through our atmosphere and pick out its different gases.\nIn 2021, Faherty found there were\nnearly 2,000 stars\nwithin 300 light-years of Earth that could potentially be able to see such a transit. \"It's a good haul of worlds,\" she says.\nThe best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would \"be an indication of a stable liquid ocean\".\nYou might also like:\nThe weird aliens of the 19th Century\nAre aliens real? Here's what we know\nWhat life might be like in oceans on other worlds\nNitrogen dioxide could also provide some clues\nthat our planet was inhabited by an intelligent lifeform. The gas is \"basically a byproduct of combustion\", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. \"So they might deduce we are burning stuff here.\"\nChlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. \"We're pretty sure they can only be produced by technology,\" says Macy Huston, an astronomer at the University of California, Berkeley in the US. (\nRead more about\nhow we might also be able to spot alien life from their pollution\n.)\nBy 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes\nOne of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights\ncould be detectable\nin a planet's atmosphere. \"It has very sharp spectral features,\" says Beatty. \"You'd never get that through a natural process.\"\nEarth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than\n1% of the Earth's surface is covered by cities\n. It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty.\nBut alien civilisations with more advanced telescopes might already be able to spot us. \"It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now,\" he says.\nEven if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. \"As long as you can see a point of light, you can analyse it,\" says Jiang,\nwho used a spacecraft in our Solar System\nin 2018 to demonstrate the technique on Earth.\nAll of this raises the question of whether we really want to be so noticeable. \"In movies we always get invaded,\" says Beatty.\nIn reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a\nfamous high-powered radio signal\ncontaining a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. \"I'm not really worried about Independence Day scenarios,\" says Beth Biller, an astronomer at the University of Edinburgh in the UK.\nGetty Images\nAstronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)\nAs humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot\nthe cloud of satellites\norbiting our planet. We would need to have \"a billion times what we have now, which sounds like a lot,\" he says. \"But we went from one car to over a billion cars in a few decades.\"\nPerhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a\nhandful of further attempts\n. \"If it were just up to me, I'd be broadcasting our existence and hoping someone would answer,\" says Rimmer. \"But that's just my opinion. This is a decision that I think should be made globally.\"\nIf the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. \"That would be the main way to get noticed, if we wanted to,\" he says.\nFor the time being, signs of our existence are more modest, but still detectable. \"They don't need miracles,\" says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. \"They just need the technology we have, but on a larger scale.\"\nThe real question we should ask: is anyone looking our way to notice?\n--\nIf you liked this story, \nsign up for The Essential List newsletter\n – a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday.\nJoin one million Future fans by liking us on\nFacebook\n, or follow us on\nTwitter\nor\nInstagram\n.","attrs_markdown":"[Skip to content](https:\/\/www.bbc.com\/future\/article\/20231024-how-aliens-might-detect-our-existence-on-earth#main-content)\n\n[Register](https:\/\/session.bbc.com\/session?action=register&userOrigin=BBCS_BBC&ptrt=https%3A%2F%2Fwww.bbc.com%2Ffuture%2Farticle%2F20231024-how-aliens-might-detect-our-existence-on-earth)\n\n[Sign In](https:\/\/session.bbc.com\/session?userOrigin=BBCS_BBC&ptrt=https%3A%2F%2Fwww.bbc.com%2Ffuture%2Farticle%2F20231024-how-aliens-might-detect-our-existence-on-earth)\n\n- [Home](https:\/\/www.bbc.com\/)\n- [News](https:\/\/www.bbc.com\/news)\n- [Sport](https:\/\/www.bbc.com\/sport)\n- [Business](https:\/\/www.bbc.com\/business)\n- [Technology](https:\/\/www.bbc.com\/technology)\n- [Health](https:\/\/www.bbc.com\/health)\n- [Culture](https:\/\/www.bbc.com\/culture)\n- [Arts](https:\/\/www.bbc.com\/arts)\n- [Travel](https:\/\/www.bbc.com\/travel)\n- [Earth](https:\/\/www.bbc.com\/future-planet)\n- [Audio](https:\/\/www.bbc.com\/audio)\n- [Video](https:\/\/www.bbc.com\/video)\n- [Live](https:\/\/www.bbc.com\/live)\n\n- [Home](https:\/\/www.bbc.com\/home)\n- [News](https:\/\/www.bbc.com\/news)\n  - [US & Canada](https:\/\/www.bbc.com\/news\/us-canada)\n  - [UK](https:\/\/www.bbc.com\/news\/uk)\n    - [UK Politics](https:\/\/www.bbc.com\/news\/politics)\n    - [England](https:\/\/www.bbc.com\/news\/england)\n    - [N. Ireland](https:\/\/www.bbc.com\/news\/northern_ireland)\n      - [N. Ireland Politics](https:\/\/www.bbc.com\/news\/northern_ireland\/northern_ireland_politics)\n    - [Scotland](https:\/\/www.bbc.com\/news\/scotland)\n      - [Scotland Politics](https:\/\/www.bbc.com\/news\/scotland\/scotland_politics)\n    - [Wales](https:\/\/www.bbc.com\/news\/wales)\n      - [Wales Politics](https:\/\/www.bbc.com\/news\/wales\/wales_politics)\n  - [Africa](https:\/\/www.bbc.com\/news\/world\/africa)\n  - [Asia](https:\/\/www.bbc.com\/news\/world\/asia)\n    - [China](https:\/\/www.bbc.com\/news\/world\/asia\/china)\n    - [India](https:\/\/www.bbc.com\/news\/world\/asia\/india)\n  - [Australia](https:\/\/www.bbc.com\/news\/world\/australia)\n  - [Europe](https:\/\/www.bbc.com\/news\/world\/europe)\n  - [Latin America](https:\/\/www.bbc.com\/news\/world\/latin_america)\n  - [Middle East](https:\/\/www.bbc.com\/news\/world\/middle_east)\n  - [In Pictures](https:\/\/www.bbc.com\/news\/in_pictures)\n  - [BBC InDepth](https:\/\/www.bbc.com\/news\/bbcindepth)\n  - [BBC Verify](https:\/\/www.bbc.com\/news\/bbcverify)\n- [Sport](https:\/\/www.bbc.com\/sport)\n- [Business](https:\/\/www.bbc.com\/business)\n  - [World of Business](https:\/\/www.bbc.com\/business\/world-of-business)\n  - [Technology of Business](https:\/\/www.bbc.com\/business\/technology-of-business)\n  - [NYSE Opening Bell](https:\/\/www.bbc.com\/business\/opening-bell)\n- [Technology](https:\/\/www.bbc.com\/technology)\n  - [Artificial Intelligence](https:\/\/www.bbc.com\/technology\/artificial-intelligence)\n  - [AI v the Mind](https:\/\/www.bbc.com\/technology\/ai-v-the-mind)\n- [Health](https:\/\/www.bbc.com\/health)\n- [Culture](https:\/\/www.bbc.com\/culture)\n  - [Film & TV](https:\/\/www.bbc.com\/culture\/film-tv)\n  - [Music](https:\/\/www.bbc.com\/culture\/music)\n  - [Art & Design](https:\/\/www.bbc.com\/culture\/art)\n  - [Style](https:\/\/www.bbc.com\/culture\/style)\n  - [Books](https:\/\/www.bbc.com\/culture\/books)\n  - [Entertainment News](https:\/\/www.bbc.com\/culture\/entertainment-news)\n- [Arts](https:\/\/www.bbc.com\/arts)\n  - [Arts in Motion](https:\/\/www.bbc.com\/arts\/arts-in-motion)\n- [Travel](https:\/\/www.bbc.com\/travel)\n  - [Destinations](https:\/\/www.bbc.com\/travel\/destinations)\n    - [Africa](https:\/\/www.bbc.com\/travel\/destinations\/africa)\n    - [Antarctica](https:\/\/www.bbc.com\/travel\/destinations\/antarctica)\n    - [Asia](https:\/\/www.bbc.com\/travel\/destinations\/asia)\n    - [Australia and Pacific](https:\/\/www.bbc.com\/travel\/destinations\/australia-and-pacific)\n    - [Caribbean & Bermuda](https:\/\/www.bbc.com\/travel\/destinations\/caribbean)\n    - [Central America](https:\/\/www.bbc.com\/travel\/destinations\/central-america)\n    - [Europe](https:\/\/www.bbc.com\/travel\/destinations\/europe)\n    - [Middle East](https:\/\/www.bbc.com\/travel\/destinations\/middle-east)\n    - [North America](https:\/\/www.bbc.com\/travel\/destinations\/north-america)\n    - [South America](https:\/\/www.bbc.com\/travel\/destinations\/south-america)\n  - [World’s Table](https:\/\/www.bbc.com\/travel\/worlds-table)\n  - [Culture & Experiences](https:\/\/www.bbc.com\/travel\/cultural-experiences)\n  - [Adventures](https:\/\/www.bbc.com\/travel\/adventures)\n  - [The SpeciaList](https:\/\/www.bbc.com\/travel\/specialist)\n- [Earth](https:\/\/www.bbc.com\/future-planet)\n  - [Science](https:\/\/www.bbc.com\/innovation\/science)\n  - [Natural Wonders](https:\/\/www.bbc.com\/future-planet\/natural-wonders)\n  - [Climate Solutions](https:\/\/www.bbc.com\/future-planet\/solutions)\n  - [Sustainable Business](https:\/\/www.bbc.com\/future-planet\/sustainable-business)\n  - [Green Living](https:\/\/www.bbc.com\/future-planet\/green-living)\n- [Audio](https:\/\/www.bbc.com\/audio)\n  - [Podcast Categories](https:\/\/www.bbc.com\/audio\/categories)\n  - [Radio](https:\/\/www.bbc.com\/audio\/stations)\n  - [Audio FAQs](https:\/\/www.bbc.com\/undefined)\n- [Video](https:\/\/www.bbc.com\/video)\n  - [BBC Maestro](https:\/\/www.bbc.com\/video\/bbc-maestro)\n  - [Discover the World](https:\/\/www.bbc.com\/video\/discover-the-world)\n- [Live](https:\/\/www.bbc.com\/live)\n  - [Live News](https:\/\/www.bbc.com\/live\/news)\n  - [Live Sport](https:\/\/www.bbc.com\/live\/sport)\n\n[Home](https:\/\/www.bbc.com\/)\n\nNews\n\n[Sport](https:\/\/www.bbc.com\/sport)\n\nBusiness\n\nTechnology\n\n[Health](https:\/\/www.bbc.com\/health)\n\nCulture\n\nArts\n\nTravel\n\nEarth\n\nAudio\n\nVideo\n\nLive\n\n[Weather](https:\/\/www.bbc.com\/weather)\n\n[Newsletters](https:\/\/www.bbc.com\/newsletters)\n\n# Why aliens might already know that humans exist\n25 October 2023\n\nShare\n\nSave\n\nJonathan O'CallaghanFeatures correspondent\n\nShare\n\nSave\n\n![Nasa\/JSC A view of the Moon orbiting the Earth taken from 3.9 million miles away by the Galileo spacecraft (Credit: Nasa\/JSC)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjfr2.jpg.webp)Nasa\/JSC\n\nThis view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa\/JSC)\n\n**Alien astronomers might be looking in our direction from distant planets. What would they see?**\n\nWe've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have [identified a few possible candidates](https:\/\/iopscience.iop.org\/article\/10.3847\/1538-4357\/ac5c4e) for where life might conceivably exist elsewhere in the Universe, along with the odd [mysterious signal](https:\/\/iopscience.iop.org\/article\/10.3847\/2515-5172\/ac9408), there is yet to be any concrete evidence of alien life out there.\n\nThis article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, [**Doctor Who**](https:\/\/www.bbc.com\/culture\/article\/20230925-time-travel-to-the-tardis-11-facts-you-need-to-know-about-doctor-who-before-watching).\n\nBut what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth?\n\nThat's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. \"Hold the mirror up to yourself in space, and what would they see of us?\" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. \"We're looking. That means other worlds might be looking too.\"\n\nTo date, we have found [more than 5,500 planets](https:\/\/exoplanets.nasa.gov\/discovery\/exoplanet-catalog\/) orbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy – [trillions of worlds are likely scattered throughout the Milky Way](https:\/\/exoplanets.nasa.gov\/discovery\/how-we-find-and-characterize\/). Upon some of these worlds we have started to hunt both for the [chemical signatures in their atmospheres](https:\/\/exoplanets.nasa.gov\/search-for-life\/can-we-find-life\/) that might indicate biological activity and even [technosignatures](https:\/\/www.nature.com\/articles\/s41550-022-01872-z) that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction.\n\nEarth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. \"They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers,\" he says.\n\nWe continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. \"Radio stations don't want to broadcast into space,\" says Thomas Beatty, an astronomer at the University of Wisconsin in the US. \"They want to broadcast to the ground.\" Other more modern forms of communication, like mobile phone signals, are [unlikely to be detectable](https:\/\/arxiv.org\/abs\/2304.13779).\n\n![Nasa\/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa\/JSC)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjhl7.jpg.webp)Nasa\/JSC\n\nThe light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa\/JSC)\n\nBut not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's [Voyager 1 spacecraft](https:\/\/www.bbc.com\/future\/article\/20170818-voyager-inside-the-worlds-greatest-space-mission), is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with.\n\nIn April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might [reach other stars](https:\/\/arxiv.org\/abs\/2304.07400) as they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. \"The signal would definitely show up as artificial,\" says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study.\n\nBut what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun, [known as a transit](https:\/\/www.bbc.co.uk\/news\/science-environment-24642603), they could see sunlight passing through our atmosphere and pick out its different gases.\n\nIn 2021, Faherty found there were [nearly 2,000 stars](https:\/\/www.nature.com\/articles\/s41586-021-03596-y) within 300 light-years of Earth that could potentially be able to see such a transit. \"It's a good haul of worlds,\" she says.\n\nThe best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would \"be an indication of a stable liquid ocean\".\n\n*You might also like:*\n\n- [The weird aliens of the 19th Century](https:\/\/www.bbc.com\/future\/article\/20231019-the-weird-aliens-of-early-science-fiction)\n- [Are aliens real? Here's what we know](https:\/\/www.bbc.com\/future\/article\/20231020-seven-surprising-things-we-now-know-about-aliens)\n- [What life might be like in oceans on other worlds](https:\/\/www.bbc.com\/future\/article\/20190926-what-life-might-be-like-in-the-alien-oceans)\n\n[Nitrogen dioxide could also provide some clues](https:\/\/www.nasa.gov\/news-release\/nasa-study-to-find-an-extraterrestrial-civilization-pollution-could-be-the-solution\/) that our planet was inhabited by an intelligent lifeform. The gas is \"basically a byproduct of combustion\", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. \"So they might deduce we are burning stuff here.\"\n\nChlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. \"We're pretty sure they can only be produced by technology,\" says Macy Huston, an astronomer at the University of California, Berkeley in the US. (*Read more about* [*how we might also be able to spot alien life from their pollution*](https:\/\/www.bbc.com\/future\/article\/20231023-could-we-find-alien-life-via-their-pollution).)\n\nBy 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes\n\nOne of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights [could be detectable](https:\/\/arxiv.org\/abs\/2105.09990) in a planet's atmosphere. \"It has very sharp spectral features,\" says Beatty. \"You'd never get that through a natural process.\"\n\nEarth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than [1% of the Earth's surface is covered by cities](https:\/\/essd.copernicus.org\/articles\/14\/517\/2022\/). It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty.\n\nBut alien civilisations with more advanced telescopes might already be able to spot us. \"It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now,\" he says.\n\nEven if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. \"As long as you can see a point of light, you can analyse it,\" says Jiang, [who used a spacecraft in our Solar System](https:\/\/arxiv.org\/pdf\/1908.04350.pdf) in 2018 to demonstrate the technique on Earth.\n\nAll of this raises the question of whether we really want to be so noticeable. \"In movies we always get invaded,\" says Beatty.\n\nIn reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a [famous high-powered radio signal](https:\/\/www.bbc.co.uk\/programmes\/p053d1cx) containing a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. \"I'm not really worried about Independence Day scenarios,\" says Beth Biller, an astronomer at the University of Edinburgh in the UK.\n\n![Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjjgj.jpg.webp)Getty Images\n\nAstronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)\n\nAs humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot [the cloud of satellites](https:\/\/arxiv.org\/abs\/1802.07723) orbiting our planet. We would need to have \"a billion times what we have now, which sounds like a lot,\" he says. \"But we went from one car to over a billion cars in a few decades.\"\n\nPerhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a [handful of further attempts](https:\/\/en.wikipedia.org\/wiki\/Active_SETI). \"If it were just up to me, I'd be broadcasting our existence and hoping someone would answer,\" says Rimmer. \"But that's just my opinion. This is a decision that I think should be made globally.\"\n\nIf the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. \"That would be the main way to get noticed, if we wanted to,\" he says.\n\nFor the time being, signs of our existence are more modest, but still detectable. \"They don't need miracles,\" says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. \"They just need the technology we have, but on a larger scale.\"\n\nThe real question we should ask: is anyone looking our way to notice?\n\n\\--\n\n*If you liked this story,* [*sign up for The Essential List newsletter*](https:\/\/cloud.email.bbc.com\/SignUp10_08?&at_bbc_team=studios&at_medium=Onsite&at_objective=acquisition&at_ptr_name=bbc.com&at_link_origin=featuresarticle&at_campaign=essentiallist&at_campaign_type=owned) *– a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday.*\n\n*Join one million Future fans by liking us on* [*Facebook*](https:\/\/www.facebook.com\/BBCFuture\/)*, or follow us on* [*Twitter*](https:\/\/twitter.com\/BBC_Future) *or* [*Instagram*](https:\/\/www.instagram.com\/bbcfuture_official\/)*.*\n\n[Extraterrestrial life](https:\/\/www.bbc.com\/future\/tags\/extraterrestriallife)\n\n[Space](https:\/\/www.bbc.com\/future\/tags\/space)\n\n[Universe](https:\/\/www.bbc.com\/future\/tags\/universe)\n\n[Science](https:\/\/www.bbc.com\/future\/tags\/science)\n\n***\nWatch\n\n[![How can rollercoasters hold so much weight?](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0mb84m2.jpg.webp) How can rollercoasters hold so much weight? Rollercoasters send our hearts racing and stomachs dropping. Hannah Fry dives into the science of how they work. Science](https:\/\/www.bbc.com\/reel\/video\/p0mb832b\/watch)\n\n[![Explaining how a touchscreen works with a sausage](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0lv0kz9.jpg.webp) Explaining how a touchscreen works with a sausage British mathematician Hannah Fry digs into the science of touchscreens. Science](https:\/\/www.bbc.com\/reel\/video\/p0lv0hqk\/watch)\n\n[![Listen to the Sun like never before](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0lhmlvq.jpg.webp) Listen to the Sun like never before A Nasa exhibit lets you hear the Sun's raw power, turning solar data into an unforgettable soundscape. Space](https:\/\/www.bbc.com\/reel\/video\/p0lh9vm3\/watch)\n\n[![What's inside a black hole?](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0l39hnr.jpg.webp) What's inside a black hole? Black holes are one of the mysteries of the universe where all the laws of nature as we know them stop working. Science](https:\/\/www.bbc.com\/reel\/video\/p0l39967\/watch)\n\n[![Getty Images 1224663560](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0kzkbfc.jpg.webp) Using bubbles to remove forever chemicals from our water BBC Click visits a UK research team working on a solution to remove toxic chemicals known as PFAS from water. Science](https:\/\/www.bbc.com\/reel\/video\/p0kyqdqb\/watch)\n\n[![How sex with Neanderthals changed us forever](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0kytt3p.jpg.webp) How sex with Neanderthals changed us forever According to biologists, modern humans and Neanderthals shouldn't have been able to breed. But they did. Science](https:\/\/www.bbc.com\/reel\/video\/p0kytlx7\/watch)\n\n[![Theory of Evolution: How did Charles Darwin come up with it?](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0kqp90m.jpg.webp) Theory of Evolution: How did Charles Darwin come up with it? The British naturalist embarked on an extraordinary journey, did hundreds of experiments, and wrote for 20 years. Science](https:\/\/www.bbc.com\/reel\/video\/p0kqkmz3\/watch)\n\n[!['Homo juluensis': Possible new ancient human identified](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0kgwsjn.jpg.webp) Homo juluensis: Possible 'new ancient human' identified Researchers may have identified a new human species that lived around 300,000 years ago in Asia. Science](https:\/\/www.bbc.com\/reel\/video\/p0kftjyg\/watch)\n\n[![How Arctic communities protect themselves from avalanches](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0kfy5cr.jpg.webp) How Arctic communities protect themselves from avalanches BBC Click finds out how local communities in Svalbard use technology to combat avalanches and heavy snowfall. Science](https:\/\/www.bbc.com\/reel\/video\/p0kcpnm6\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![How space changed my body](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0j1h2b6.jpg.webp) Astronaut Peggy Whitson: How space changed my body Peggy Whitson has spent 675 days in space, more than any other American. Here's how it affected her body. Space](https:\/\/www.bbc.com\/reel\/video\/p0hxbksd\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Jupiter stuns in new Juno pictures](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0k6xjz9.jpg.webp) See Nasa's spectacular new images of Jupiter The photos created by citizen scientists using Nasa's data have contributed to new discoveries about Jupiter. Space](https:\/\/www.bbc.com\/reel\/video\/p0k6x7q8\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Why our planet's crust has tides too](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jt9gtk.jpg.webp) Earth tides: Why our planet's crust has tides too How do they differ from the ocean? A geophysicist breaks it down for us. Weather & science](https:\/\/www.bbc.com\/reel\/video\/p0jt8x5z\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Is Earth getting a 'mini moon' this fall?](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jssrtv.jpg.webp) The science behind the 'mini moon' entering Earth's orbit An asteroid is going to circle our planet for two months this autumn before going on its way. Weather & science](https:\/\/www.bbc.com\/reel\/video\/p0jsl446\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Screenshot 2024 08 22 at 8 51 13 PM](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jp0p4j.png.webp) New Nasa sonifications: Listen to the sound of the Universe Nasa has released new 'sonifications' of the Universe on the 25th anniversary of Chandra, its X-ray Observatory. Space](https:\/\/www.bbc.com\/reel\/video\/p0jlbpl3\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Uncovering the sunken relics of an ancient city](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jnbpvk.jpg.webp) Uncovering the sunken relics of an ancient city Bettany Hughes goes underwater in search of ancient archaeological finds in historic Sozopol, Bulgaria. Archaeology](https:\/\/www.bbc.com\/reel\/video\/p0jnbll0\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Screenshot 2024 08 20 at 2 00 51 PM min](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jklf59.png.webp) In Australia, sea lions help researchers map the ocean floor Researchers in Australia put cameras on sea lions' backs to help them map the elusive ocean floor. Earth](https:\/\/www.bbc.com\/reel\/video\/p0jkkyc6\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![The scientists drilling into an anctive Icelandic volcano](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0jhk026.jpg.webp) The scientists drilling into an active Icelandic volcano Scientists are preparing to drill into the rock of an Icelandic volcano to learn more about how volcanoes behave. Climate solutions](https:\/\/www.bbc.com\/reel\/video\/p0jgsff2\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![Why we may have misunderstood the Universe](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0j882d0.jpg.webp) Why we may have misunderstood the Universe Research by a Nobel Prize winning astrophysicist suggests we have been wrong about the expansion of our Universe. Science](https:\/\/www.bbc.com\/reel\/video\/p0j83nwv\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![What living in space could look like](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0hxt8vj.jpg.webp) Are inflatable habitats the future of life in space? As the reality of civilian space travel closes-in, engineers explore inflatable habitats. Space](https:\/\/www.bbc.com\/reel\/video\/p0hxszh2\/watch)\n\n[![](https:\/\/static.files.bbci.co.uk\/bbcdotcom\/web\/20260309-121341-5f81352518-web-2.41.1-2\/grey-placeholder.png)![A rare star explosion is coming](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0hvnlp0.jpg.webp) We're about to witness a once-in-a-lifetime star explosion An extremely rare stellar explosion is about to happen and we will be able to witness it with the naked eye. Space](https:\/\/www.bbc.com\/reel\/video\/p0hvn69l\/watch)\n\n***\nMore from the BBC\n\n[9 hrs ago ![A bus in Nepal picks its way along a road on a hillside that is crumbling away beneath the road (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0n8cpg6.jpg.webp) When the Earth moves, AI can spot it Sudden and unexpected, landslides and avalanches claim thousands of lives each year and cause billions of dollars in damage. What if we could see them coming? 9 hrs ago](https:\/\/www.bbc.com\/future\/article\/20260323-the-ai-that-warns-people-about-landslides-and-avalanches)\n\n[1 day ago ![A Sumerian tablet from around 3200BC some of the earliest known mathematical exercises (Credit: Cuneiform Digital Library Initiative)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0n7xpgv.jpg.webp) The ancient reason there are 60 minutes in an hour A mysterious 5,000-year-old decision led directly to how we still count time today. 1 day ago](https:\/\/www.bbc.com\/future\/article\/20260320-the-ancient-reason-there-are-60-minutes-in-an-hour-and-60-seconds-in-a-minute)\n\n[3 days ago ![A close up of a woman's mouth as she places a nut between her teeth (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0n7vsfj.jpg.webp) Don't count calories. Try eating smarter instead The time of day you have a meal, how fast you scoff your food and even how much you chew it can affect how many calories you get from it. 3 days ago](https:\/\/www.bbc.com\/future\/article\/20260320-counting-calories-doesnt-work-try-eating-smarter-instead)\n\n[5 days ago ![A mother holding a child on her lap as he eats breakfast and she writes on a paper (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0n7f73g.jpg.webp) Feeling drained? Blame these forms of hidden work Women are still taking on most of the cognitive burden of running a household. Understanding why is the key to reducing burnout. 5 days ago](https:\/\/www.bbc.com\/future\/article\/20260318-eight-types-of-mental-load-that-leave-women-drained)\n\n[15 Mar 2026 ![A man in a blue checked shirt touching bellies with a pregnant woman in a grey dress (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480x270\/p0n6jgft.jpg.webp) This baffling syndrome makes fathers feel pregnant Couvade syndrome is changing how scientists think about the role of men in childbearing. 15 Mar 2026](https:\/\/www.bbc.com\/future\/article\/20260313-the-mysteries-of-couvade-syndrome)\n***\n- [Home](https:\/\/www.bbc.com\/)\n- [News](https:\/\/www.bbc.com\/news)\n- [Sport](https:\/\/www.bbc.com\/sport)\n- [Business](https:\/\/www.bbc.com\/business)\n- [Technology](https:\/\/www.bbc.com\/technology)\n- [Health](https:\/\/www.bbc.com\/health)\n- [Culture](https:\/\/www.bbc.com\/culture)\n- [Arts](https:\/\/www.bbc.com\/arts)\n- [Travel](https:\/\/www.bbc.com\/travel)\n- [Earth](https:\/\/www.bbc.com\/future-planet)\n- [Audio](https:\/\/www.bbc.com\/audio)\n- [Video](https:\/\/www.bbc.com\/video)\n- [Live](https:\/\/www.bbc.com\/live)\n- [Weather](https:\/\/www.bbc.com\/weather)\n- [BBC Shop](https:\/\/shop.bbc.com\/)\n- [BritBox](https:\/\/www.britbox.com\/?utm_source=bbc.com&utm_medium=referral&utm_campaign=footer)\n\nBBC in other languages\n\n### The BBC is in multiple languages\n#### Read the BBC In your own language\n[Oduu Afaan Oromootiin](https:\/\/www.bbc.com\/afaanoromoo)\n\n[Amharic ዜና በአማርኛ](https:\/\/www.bbc.com\/amharic)\n\n[Arabic عربي](https:\/\/www.bbc.com\/arabic)\n\n[Azeri AZƏRBAYCAN](https:\/\/www.bbc.com\/azeri)\n\n[Bangla বাংলা](https:\/\/www.bbc.com\/bengali)\n\n[Burmese မြန်မာ](https:\/\/www.bbc.com\/burmese)\n\n[Chinese 中文网](https:\/\/www.bbc.com\/zhongwen\/simp)\n\n[Dari دری](https:\/\/www.bbc.com\/dari)\n\n[French AFRIQUE](https:\/\/www.bbc.com\/afrique)\n\n[Hausa HAUSA](https:\/\/www.bbc.com\/hausa)\n\n[Hindi हिन्दी](https:\/\/www.bbc.com\/hindi)\n\n[Gaelic NAIDHEACHDAN](https:\/\/www.bbc.com\/naidheachdan)\n\n[Gujarati ગુજરાતીમાં સમાચાર](https:\/\/www.bbc.com\/gujarati)\n\n[Igbo AKỤKỌ N’IGBO](https:\/\/www.bbc.com\/igbo)\n\n[Indonesian INDONESIA](https:\/\/www.bbc.com\/indonesia)\n\n[Japanese 日本語](https:\/\/www.bbc.com\/japanese)\n\n[Kinyarwanda GAHUZA](https:\/\/www.bbc.com\/gahuza)\n\n[Kirundi KIRUNDI](https:\/\/www.bbc.com\/gahuza)\n\n[Korean 한국어](https:\/\/www.bbc.com\/korean)\n\n[Kyrgyz Кыргыз](https:\/\/www.bbc.com\/kyrgyz)\n\n[Marathi मराठी](https:\/\/www.bbc.com\/marathi)\n\n[Nepali नेपाली](https:\/\/www.bbc.com\/nepali)\n\n[Noticias para hispanoparlantes](https:\/\/www.bbc.com\/mundo)\n\n[Pashto پښتو](https:\/\/www.bbc.com\/pashto)\n\n[Persian فارسی](https:\/\/www.bbc.com\/persian)\n\n[Pidgin](https:\/\/www.bbc.com\/pidgin)\n\n[Polish PO POLSKU](https:\/\/www.bbc.com\/polska)\n\n[Portuguese BRASIL](https:\/\/www.bbc.com\/portuguese)\n\n[Punjabi ਪੰਜਾਬੀ ਖ਼ਬਰਾਂ](https:\/\/www.bbc.com\/punjabi)\n\n[Russian НА РУССКОМ](https:\/\/www.bbc.com\/russian)\n\n[Serbian NA SRPSKOM](https:\/\/www.bbc.com\/serbian\/lat)\n\n[Sinhala සිංහල](https:\/\/www.bbc.com\/sinhala)\n\n[Somali SOMALI](https:\/\/www.bbc.com\/somali)\n\n[Swahili HABARI KWA KISWAHILI](https:\/\/www.bbc.com\/swahili)\n\n[Tamil தமிழில் செய்திகள்](https:\/\/www.bbc.com\/tamil)\n\n[Telugu తెలుగు వార్తలు](https:\/\/www.bbc.com\/telugu)\n\n[Thai ข่าวภาษาไทย](https:\/\/www.bbc.com\/thai)\n\n[Tigrinya ዜና ብትግርኛ](https:\/\/www.bbc.com\/tigrinya)\n\n[Turkish TÜRKÇE](https:\/\/www.bbc.com\/turkce)\n\n[Ukrainian УКРАЇНСЬКA](https:\/\/www.bbc.com\/ukrainian)\n\n[Urdu اردو](https:\/\/www.bbc.com\/urdu)\n\n[Uzbek O'ZBEK](https:\/\/www.bbc.com\/uzbek)\n\n[Vietnamese TIẾNG VIỆT](https:\/\/www.bbc.com\/vietnamese)\n\n[Welsh NEWYDDION](https:\/\/www.bbc.com\/cymrufyw)\n\n[Yoruba ÌRÒYÌN NÍ YORÙBÁ](https:\/\/www.bbc.com\/yoruba)\n\nFollow BBC on:\n\n- [Terms of Use](https:\/\/www.bbc.com\/pages\/terms-of-use)\n- [Subscription Terms](https:\/\/www.bbc.com\/pages\/subscription-terms)\n- [About the BBC](https:\/\/www.bbc.co.uk\/aboutthebbc)\n- [Privacy Policy](https:\/\/www.bbc.com\/pages\/privacy-policy)\n- [Cookies](https:\/\/www.bbc.com\/usingthebbc\/cookies\/)\n- [Accessibility Help](https:\/\/www.bbc.co.uk\/accessibility\/)\n- [Contact the BBC](https:\/\/www.bbc.co.uk\/contact)\n- [Advertise with us](https:\/\/advertising.bbcstudios.com\/)\n- [Do not share or sell my info](https:\/\/www.bbc.com\/usingthebbc\/cookies\/how-can-i-change-my-bbc-cookie-settings\/)\n- [BBC.com Help & FAQs](https:\/\/help.bbc.com\/hc\/)\n- [Content Index](https:\/\/www.bbc.com\/pages\/content-index)\n- [Set Preferred Source](https:\/\/www.bbc.com\/future\/article\/20260128-how-to-make-google-put-trusted-sources-up-top-when-you-search)\n\nCopyright 2026 BBC. All rights reserved. The BBC is not responsible for the content of external sites. [**Read about our approach to external linking.**](https:\/\/www.bbc.co.uk\/editorialguidelines\/guidance\/feeds-and-links)","attrs_readable_markdown":"25 October 2023\n\nJonathan O'CallaghanFeatures correspondent\n\n![Nasa\/JSC A view of the Moon orbiting the Earth taken from 3.9 million miles away by the Galileo spacecraft (Credit: Nasa\/JSC)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjfr2.jpg.webp)Nasa\/JSC\n\nThis view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa\/JSC)\n\n**Alien astronomers might be looking in our direction from distant planets. What would they see?**\n\nWe've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have [identified a few possible candidates](https:\/\/iopscience.iop.org\/article\/10.3847\/1538-4357\/ac5c4e) for where life might conceivably exist elsewhere in the Universe, along with the odd [mysterious signal](https:\/\/iopscience.iop.org\/article\/10.3847\/2515-5172\/ac9408), there is yet to be any concrete evidence of alien life out there.\n\nThis article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, [**Doctor Who**](https:\/\/www.bbc.com\/culture\/article\/20230925-time-travel-to-the-tardis-11-facts-you-need-to-know-about-doctor-who-before-watching).\n\nBut what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth?\n\nThat's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. \"Hold the mirror up to yourself in space, and what would they see of us?\" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. \"We're looking. That means other worlds might be looking too.\"\n\nTo date, we have found [more than 5,500 planets](https:\/\/exoplanets.nasa.gov\/discovery\/exoplanet-catalog\/) orbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy – [trillions of worlds are likely scattered throughout the Milky Way](https:\/\/exoplanets.nasa.gov\/discovery\/how-we-find-and-characterize\/). Upon some of these worlds we have started to hunt both for the [chemical signatures in their atmospheres](https:\/\/exoplanets.nasa.gov\/search-for-life\/can-we-find-life\/) that might indicate biological activity and even [technosignatures](https:\/\/www.nature.com\/articles\/s41550-022-01872-z) that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction.\n\nEarth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. \"They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers,\" he says.\n\nWe continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. \"Radio stations don't want to broadcast into space,\" says Thomas Beatty, an astronomer at the University of Wisconsin in the US. \"They want to broadcast to the ground.\" Other more modern forms of communication, like mobile phone signals, are [unlikely to be detectable](https:\/\/arxiv.org\/abs\/2304.13779).\n\n![Nasa\/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa\/JSC)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjhl7.jpg.webp)Nasa\/JSC\n\nThe light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa\/JSC)\n\nBut not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's [Voyager 1 spacecraft](https:\/\/www.bbc.com\/future\/article\/20170818-voyager-inside-the-worlds-greatest-space-mission), is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with.\n\nIn April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might [reach other stars](https:\/\/arxiv.org\/abs\/2304.07400) as they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. \"The signal would definitely show up as artificial,\" says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study.\n\nBut what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun, [known as a transit](https:\/\/www.bbc.co.uk\/news\/science-environment-24642603), they could see sunlight passing through our atmosphere and pick out its different gases.\n\nIn 2021, Faherty found there were [nearly 2,000 stars](https:\/\/www.nature.com\/articles\/s41586-021-03596-y) within 300 light-years of Earth that could potentially be able to see such a transit. \"It's a good haul of worlds,\" she says.\n\nThe best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would \"be an indication of a stable liquid ocean\".\n\n*You might also like:*\n\n- [The weird aliens of the 19th Century](https:\/\/www.bbc.com\/future\/article\/20231019-the-weird-aliens-of-early-science-fiction)\n- [Are aliens real? Here's what we know](https:\/\/www.bbc.com\/future\/article\/20231020-seven-surprising-things-we-now-know-about-aliens)\n- [What life might be like in oceans on other worlds](https:\/\/www.bbc.com\/future\/article\/20190926-what-life-might-be-like-in-the-alien-oceans)\n\n[Nitrogen dioxide could also provide some clues](https:\/\/www.nasa.gov\/news-release\/nasa-study-to-find-an-extraterrestrial-civilization-pollution-could-be-the-solution\/) that our planet was inhabited by an intelligent lifeform. The gas is \"basically a byproduct of combustion\", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. \"So they might deduce we are burning stuff here.\"\n\nChlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. \"We're pretty sure they can only be produced by technology,\" says Macy Huston, an astronomer at the University of California, Berkeley in the US. (*Read more about* [*how we might also be able to spot alien life from their pollution*](https:\/\/www.bbc.com\/future\/article\/20231023-could-we-find-alien-life-via-their-pollution).)\n\nBy 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes\n\nOne of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights [could be detectable](https:\/\/arxiv.org\/abs\/2105.09990) in a planet's atmosphere. \"It has very sharp spectral features,\" says Beatty. \"You'd never get that through a natural process.\"\n\nEarth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than [1% of the Earth's surface is covered by cities](https:\/\/essd.copernicus.org\/articles\/14\/517\/2022\/). It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty.\n\nBut alien civilisations with more advanced telescopes might already be able to spot us. \"It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now,\" he says.\n\nEven if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. \"As long as you can see a point of light, you can analyse it,\" says Jiang, [who used a spacecraft in our Solar System](https:\/\/arxiv.org\/pdf\/1908.04350.pdf) in 2018 to demonstrate the technique on Earth.\n\nAll of this raises the question of whether we really want to be so noticeable. \"In movies we always get invaded,\" says Beatty.\n\nIn reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a [famous high-powered radio signal](https:\/\/www.bbc.co.uk\/programmes\/p053d1cx) containing a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. \"I'm not really worried about Independence Day scenarios,\" says Beth Biller, an astronomer at the University of Edinburgh in the UK.\n\n![Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)](https:\/\/ichef.bbci.co.uk\/images\/ic\/480xn\/p0gnjjgj.jpg.webp)Getty Images\n\nAstronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)\n\nAs humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot [the cloud of satellites](https:\/\/arxiv.org\/abs\/1802.07723) orbiting our planet. We would need to have \"a billion times what we have now, which sounds like a lot,\" he says. \"But we went from one car to over a billion cars in a few decades.\"\n\nPerhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a [handful of further attempts](https:\/\/en.wikipedia.org\/wiki\/Active_SETI). \"If it were just up to me, I'd be broadcasting our existence and hoping someone would answer,\" says Rimmer. \"But that's just my opinion. This is a decision that I think should be made globally.\"\n\nIf the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. \"That would be the main way to get noticed, if we wanted to,\" he says.\n\nFor the time being, signs of our existence are more modest, but still detectable. \"They don't need miracles,\" says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. \"They just need the technology we have, but on a larger scale.\"\n\nThe real question we should ask: is anyone looking our way to notice?\n\n\\--\n\n*If you liked this story,* [*sign up for The Essential List newsletter*](https:\/\/cloud.email.bbc.com\/SignUp10_08?&at_bbc_team=studios&at_medium=Onsite&at_objective=acquisition&at_ptr_name=bbc.com&at_link_origin=featuresarticle&at_campaign=essentiallist&at_campaign_type=owned) *– a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday.*\n\n*Join one million Future fans by liking us on* [*Facebook*](https:\/\/www.facebook.com\/BBCFuture\/)*, or follow us on* [*Twitter*](https:\/\/twitter.com\/BBC_Future) *or* [*Instagram*](https:\/\/www.instagram.com\/bbcfuture_official\/)*.*","meta_canonical":null}

3. Robots.txt Check

Query:

Response:

4. Spam/Ban Check

Query:

Response:

5. Seen Status Check

ℹ️ Skipped - page is already crawled

📄

INDEXABLE

✅

CRAWLED

18 days ago

🚫

ROBOTS BLOCKED

Page Info Filters

Filter	Status	Condition	Details
HTTP status	PASS	`download_http_code = 200`	HTTP 200
Age cutoff	PASS	`download_stamp > now() - 6 MONTH`	0.6 months ago
History drop	PASS	`isNull(history_drop_reason)`	No drop reason
Spam/ban	PASS	`fh_dont_index != 1 AND ml_spam_score = 0`	ml_spam_score=0
Canonical	PASS	`meta_canonical IS NULL OR = '' OR = src_unparsed`	Not set

Page Details

Property	Value
URL	https://www.bbc.com/future/article/20231024-how-aliens-might-detect-our-existence-on-earth
Last Crawled	2026-03-24 18:45:26 (18 days ago)
First Indexed	2023-10-25 00:07:49 (2 years ago)
HTTP Status Code	200
Meta Title	Why aliens might already know that humans exist
Meta Description	Alien astronomers might be looking in our direction from distant planets. What would they see?
Meta Canonical	null
Boilerpipe Text	25 October 2023 Jonathan O'Callaghan Features correspondent Nasa/JSC This view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa/JSC) Alien astronomers might be looking in our direction from distant planets. What would they see? We've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have identified a few possible candidates for where life might conceivably exist elsewhere in the Universe, along with the odd mysterious signal , there is yet to be any concrete evidence of alien life out there. This article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, Doctor Who . But what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth? That's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. "Hold the mirror up to yourself in space, and what would they see of us?" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. "We're looking. That means other worlds might be looking too." To date, we have found more than 5,500 planets orbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy – trillions of worlds are likely scattered throughout the Milky Way . Upon some of these worlds we have started to hunt both for the chemical signatures in their atmospheres that might indicate biological activity and even technosignatures that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction. Earth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. "They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers," he says. We continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. "Radio stations don't want to broadcast into space," says Thomas Beatty, an astronomer at the University of Wisconsin in the US. "They want to broadcast to the ground." Other more modern forms of communication, like mobile phone signals, are unlikely to be detectable . Nasa/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa/JSC) But not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's Voyager 1 spacecraft , is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with. In April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might reach other stars as they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. "The signal would definitely show up as artificial," says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study. But what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun, known as a transit , they could see sunlight passing through our atmosphere and pick out its different gases. In 2021, Faherty found there were nearly 2,000 stars within 300 light-years of Earth that could potentially be able to see such a transit. "It's a good haul of worlds," she says. The best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would "be an indication of a stable liquid ocean". You might also like: The weird aliens of the 19th Century Are aliens real? Here's what we know What life might be like in oceans on other worlds Nitrogen dioxide could also provide some clues that our planet was inhabited by an intelligent lifeform. The gas is "basically a byproduct of combustion", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. "So they might deduce we are burning stuff here." Chlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. "We're pretty sure they can only be produced by technology," says Macy Huston, an astronomer at the University of California, Berkeley in the US. ( Read more about how we might also be able to spot alien life from their pollution .) By 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes One of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights could be detectable in a planet's atmosphere. "It has very sharp spectral features," says Beatty. "You'd never get that through a natural process." Earth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than 1% of the Earth's surface is covered by cities . It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty. But alien civilisations with more advanced telescopes might already be able to spot us. "It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now," he says. Even if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. "As long as you can see a point of light, you can analyse it," says Jiang, who used a spacecraft in our Solar System in 2018 to demonstrate the technique on Earth. All of this raises the question of whether we really want to be so noticeable. "In movies we always get invaded," says Beatty. In reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a famous high-powered radio signal containing a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. "I'm not really worried about Independence Day scenarios," says Beth Biller, an astronomer at the University of Edinburgh in the UK. Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images) As humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot the cloud of satellites orbiting our planet. We would need to have "a billion times what we have now, which sounds like a lot," he says. "But we went from one car to over a billion cars in a few decades." Perhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a handful of further attempts . "If it were just up to me, I'd be broadcasting our existence and hoping someone would answer," says Rimmer. "But that's just my opinion. This is a decision that I think should be made globally." If the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. "That would be the main way to get noticed, if we wanted to," he says. For the time being, signs of our existence are more modest, but still detectable. "They don't need miracles," says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. "They just need the technology we have, but on a larger scale." The real question we should ask: is anyone looking our way to notice? -- If you liked this story, sign up for The Essential List newsletter – a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday. Join one million Future fans by liking us on Facebook , or follow us on Twitter or Instagram .
Markdown	[Skip to content](https://www.bbc.com/future/article/20231024-how-aliens-might-detect-our-existence-on-earth#main-content) [Register](https://session.bbc.com/session?action=register&userOrigin=BBCS_BBC&ptrt=https%3A%2F%2Fwww.bbc.com%2Ffuture%2Farticle%2F20231024-how-aliens-might-detect-our-existence-on-earth) [Sign In](https://session.bbc.com/session?userOrigin=BBCS_BBC&ptrt=https%3A%2F%2Fwww.bbc.com%2Ffuture%2Farticle%2F20231024-how-aliens-might-detect-our-existence-on-earth) - [Home](https://www.bbc.com/) - [News](https://www.bbc.com/news) - [Sport](https://www.bbc.com/sport) - [Business](https://www.bbc.com/business) - [Technology](https://www.bbc.com/technology) - [Health](https://www.bbc.com/health) - [Culture](https://www.bbc.com/culture) - [Arts](https://www.bbc.com/arts) - [Travel](https://www.bbc.com/travel) - [Earth](https://www.bbc.com/future-planet) - [Audio](https://www.bbc.com/audio) - [Video](https://www.bbc.com/video) - [Live](https://www.bbc.com/live) - [Home](https://www.bbc.com/home) - [News](https://www.bbc.com/news) - [US & Canada](https://www.bbc.com/news/us-canada) - [UK](https://www.bbc.com/news/uk) - [UK Politics](https://www.bbc.com/news/politics) - [England](https://www.bbc.com/news/england) - [N. Ireland](https://www.bbc.com/news/northern_ireland) - [N. Ireland Politics](https://www.bbc.com/news/northern_ireland/northern_ireland_politics) - [Scotland](https://www.bbc.com/news/scotland) - [Scotland Politics](https://www.bbc.com/news/scotland/scotland_politics) - [Wales](https://www.bbc.com/news/wales) - [Wales Politics](https://www.bbc.com/news/wales/wales_politics) - [Africa](https://www.bbc.com/news/world/africa) - [Asia](https://www.bbc.com/news/world/asia) - [China](https://www.bbc.com/news/world/asia/china) - [India](https://www.bbc.com/news/world/asia/india) - [Australia](https://www.bbc.com/news/world/australia) - [Europe](https://www.bbc.com/news/world/europe) - [Latin America](https://www.bbc.com/news/world/latin_america) - [Middle East](https://www.bbc.com/news/world/middle_east) - [In Pictures](https://www.bbc.com/news/in_pictures) - [BBC InDepth](https://www.bbc.com/news/bbcindepth) - [BBC Verify](https://www.bbc.com/news/bbcverify) - [Sport](https://www.bbc.com/sport) - [Business](https://www.bbc.com/business) - [World of Business](https://www.bbc.com/business/world-of-business) - [Technology of Business](https://www.bbc.com/business/technology-of-business) - [NYSE Opening Bell](https://www.bbc.com/business/opening-bell) - [Technology](https://www.bbc.com/technology) - [Artificial Intelligence](https://www.bbc.com/technology/artificial-intelligence) - [AI v the Mind](https://www.bbc.com/technology/ai-v-the-mind) - [Health](https://www.bbc.com/health) - [Culture](https://www.bbc.com/culture) - [Film & TV](https://www.bbc.com/culture/film-tv) - [Music](https://www.bbc.com/culture/music) - [Art & Design](https://www.bbc.com/culture/art) - [Style](https://www.bbc.com/culture/style) - [Books](https://www.bbc.com/culture/books) - [Entertainment News](https://www.bbc.com/culture/entertainment-news) - [Arts](https://www.bbc.com/arts) - [Arts in Motion](https://www.bbc.com/arts/arts-in-motion) - [Travel](https://www.bbc.com/travel) - [Destinations](https://www.bbc.com/travel/destinations) - [Africa](https://www.bbc.com/travel/destinations/africa) - [Antarctica](https://www.bbc.com/travel/destinations/antarctica) - [Asia](https://www.bbc.com/travel/destinations/asia) - [Australia and Pacific](https://www.bbc.com/travel/destinations/australia-and-pacific) - [Caribbean & Bermuda](https://www.bbc.com/travel/destinations/caribbean) - [Central America](https://www.bbc.com/travel/destinations/central-america) - [Europe](https://www.bbc.com/travel/destinations/europe) - [Middle East](https://www.bbc.com/travel/destinations/middle-east) - [North America](https://www.bbc.com/travel/destinations/north-america) - [South America](https://www.bbc.com/travel/destinations/south-america) - [World’s Table](https://www.bbc.com/travel/worlds-table) - [Culture & Experiences](https://www.bbc.com/travel/cultural-experiences) - [Adventures](https://www.bbc.com/travel/adventures) - [The SpeciaList](https://www.bbc.com/travel/specialist) - [Earth](https://www.bbc.com/future-planet) - [Science](https://www.bbc.com/innovation/science) - [Natural Wonders](https://www.bbc.com/future-planet/natural-wonders) - [Climate Solutions](https://www.bbc.com/future-planet/solutions) - [Sustainable Business](https://www.bbc.com/future-planet/sustainable-business) - [Green Living](https://www.bbc.com/future-planet/green-living) - [Audio](https://www.bbc.com/audio) - [Podcast Categories](https://www.bbc.com/audio/categories) - [Radio](https://www.bbc.com/audio/stations) - [Audio FAQs](https://www.bbc.com/undefined) - [Video](https://www.bbc.com/video) - [BBC Maestro](https://www.bbc.com/video/bbc-maestro) - [Discover the World](https://www.bbc.com/video/discover-the-world) - [Live](https://www.bbc.com/live) - [Live News](https://www.bbc.com/live/news) - [Live Sport](https://www.bbc.com/live/sport) [Home](https://www.bbc.com/) News [Sport](https://www.bbc.com/sport) Business Technology [Health](https://www.bbc.com/health) Culture Arts Travel Earth Audio Video Live [Weather](https://www.bbc.com/weather) [Newsletters](https://www.bbc.com/newsletters) # Why aliens might already know that humans exist 25 October 2023 Share Save Jonathan O'CallaghanFeatures correspondent Share Save ![Nasa/JSC A view of the Moon orbiting the Earth taken from 3.9 million miles away by the Galileo spacecraft (Credit: Nasa/JSC)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjfr2.jpg.webp)Nasa/JSC This view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa/JSC) Alien astronomers might be looking in our direction from distant planets. What would they see? We've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have [identified a few possible candidates](https://iopscience.iop.org/article/10.3847/1538-4357/ac5c4e) for where life might conceivably exist elsewhere in the Universe, along with the odd [mysterious signal](https://iopscience.iop.org/article/10.3847/2515-5172/ac9408), there is yet to be any concrete evidence of alien life out there. This article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, [Doctor Who](https://www.bbc.com/culture/article/20230925-time-travel-to-the-tardis-11-facts-you-need-to-know-about-doctor-who-before-watching). But what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth? That's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. "Hold the mirror up to yourself in space, and what would they see of us?" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. "We're looking. That means other worlds might be looking too." To date, we have found [more than 5,500 planets](https://exoplanets.nasa.gov/discovery/exoplanet-catalog/) orbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy – [trillions of worlds are likely scattered throughout the Milky Way](https://exoplanets.nasa.gov/discovery/how-we-find-and-characterize/). Upon some of these worlds we have started to hunt both for the [chemical signatures in their atmospheres](https://exoplanets.nasa.gov/search-for-life/can-we-find-life/) that might indicate biological activity and even [technosignatures](https://www.nature.com/articles/s41550-022-01872-z) that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction. Earth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. "They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers," he says. We continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. "Radio stations don't want to broadcast into space," says Thomas Beatty, an astronomer at the University of Wisconsin in the US. "They want to broadcast to the ground." Other more modern forms of communication, like mobile phone signals, are [unlikely to be detectable](https://arxiv.org/abs/2304.13779). ![Nasa/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa/JSC)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjhl7.jpg.webp)Nasa/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa/JSC) But not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's [Voyager 1 spacecraft](https://www.bbc.com/future/article/20170818-voyager-inside-the-worlds-greatest-space-mission), is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with. In April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might [reach other stars](https://arxiv.org/abs/2304.07400) as they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. "The signal would definitely show up as artificial," says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study. But what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun, [known as a transit](https://www.bbc.co.uk/news/science-environment-24642603), they could see sunlight passing through our atmosphere and pick out its different gases. In 2021, Faherty found there were [nearly 2,000 stars](https://www.nature.com/articles/s41586-021-03596-y) within 300 light-years of Earth that could potentially be able to see such a transit. "It's a good haul of worlds," she says. The best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would "be an indication of a stable liquid ocean". You might also like: - [The weird aliens of the 19th Century](https://www.bbc.com/future/article/20231019-the-weird-aliens-of-early-science-fiction) - [Are aliens real? Here's what we know](https://www.bbc.com/future/article/20231020-seven-surprising-things-we-now-know-about-aliens) - [What life might be like in oceans on other worlds](https://www.bbc.com/future/article/20190926-what-life-might-be-like-in-the-alien-oceans) [Nitrogen dioxide could also provide some clues](https://www.nasa.gov/news-release/nasa-study-to-find-an-extraterrestrial-civilization-pollution-could-be-the-solution/) that our planet was inhabited by an intelligent lifeform. The gas is "basically a byproduct of combustion", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. "So they might deduce we are burning stuff here." Chlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. "We're pretty sure they can only be produced by technology," says Macy Huston, an astronomer at the University of California, Berkeley in the US. (Read more about [how we might also be able to spot alien life from their pollution](https://www.bbc.com/future/article/20231023-could-we-find-alien-life-via-their-pollution).) By 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes One of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights [could be detectable](https://arxiv.org/abs/2105.09990) in a planet's atmosphere. "It has very sharp spectral features," says Beatty. "You'd never get that through a natural process." Earth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than [1% of the Earth's surface is covered by cities](https://essd.copernicus.org/articles/14/517/2022/). It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty. But alien civilisations with more advanced telescopes might already be able to spot us. "It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now," he says. Even if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. "As long as you can see a point of light, you can analyse it," says Jiang, [who used a spacecraft in our Solar System](https://arxiv.org/pdf/1908.04350.pdf) in 2018 to demonstrate the technique on Earth. All of this raises the question of whether we really want to be so noticeable. "In movies we always get invaded," says Beatty. In reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a [famous high-powered radio signal](https://www.bbc.co.uk/programmes/p053d1cx) containing a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. "I'm not really worried about Independence Day scenarios," says Beth Biller, an astronomer at the University of Edinburgh in the UK. ![Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjjgj.jpg.webp)Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images) As humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot [the cloud of satellites](https://arxiv.org/abs/1802.07723) orbiting our planet. We would need to have "a billion times what we have now, which sounds like a lot," he says. "But we went from one car to over a billion cars in a few decades." Perhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a [handful of further attempts](https://en.wikipedia.org/wiki/Active_SETI). "If it were just up to me, I'd be broadcasting our existence and hoping someone would answer," says Rimmer. "But that's just my opinion. This is a decision that I think should be made globally." If the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. "That would be the main way to get noticed, if we wanted to," he says. For the time being, signs of our existence are more modest, but still detectable. "They don't need miracles," says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. "They just need the technology we have, but on a larger scale." The real question we should ask: is anyone looking our way to notice? \-- If you liked this story, [sign up for The Essential List newsletter](https://cloud.email.bbc.com/SignUp10_08?&at_bbc_team=studios&at_medium=Onsite&at_objective=acquisition&at_ptr_name=bbc.com&at_link_origin=featuresarticle&at_campaign=essentiallist&at_campaign_type=owned) – a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday. Join one million Future fans by liking us on [Facebook](https://www.facebook.com/BBCFuture/), or follow us on [Twitter](https://twitter.com/BBC_Future) or [Instagram](https://www.instagram.com/bbcfuture_official/). [Extraterrestrial life](https://www.bbc.com/future/tags/extraterrestriallife) [Space](https://www.bbc.com/future/tags/space) [Universe](https://www.bbc.com/future/tags/universe) [Science](https://www.bbc.com/future/tags/science) * Watch [![How can rollercoasters hold so much weight?](https://ichef.bbci.co.uk/images/ic/480x270/p0mb84m2.jpg.webp) How can rollercoasters hold so much weight? Rollercoasters send our hearts racing and stomachs dropping. Hannah Fry dives into the science of how they work. Science](https://www.bbc.com/reel/video/p0mb832b/watch) [![Explaining how a touchscreen works with a sausage](https://ichef.bbci.co.uk/images/ic/480x270/p0lv0kz9.jpg.webp) Explaining how a touchscreen works with a sausage British mathematician Hannah Fry digs into the science of touchscreens. Science](https://www.bbc.com/reel/video/p0lv0hqk/watch) [![Listen to the Sun like never before](https://ichef.bbci.co.uk/images/ic/480x270/p0lhmlvq.jpg.webp) Listen to the Sun like never before A Nasa exhibit lets you hear the Sun's raw power, turning solar data into an unforgettable soundscape. Space](https://www.bbc.com/reel/video/p0lh9vm3/watch) [![What's inside a black hole?](https://ichef.bbci.co.uk/images/ic/480x270/p0l39hnr.jpg.webp) What's inside a black hole? Black holes are one of the mysteries of the universe where all the laws of nature as we know them stop working. Science](https://www.bbc.com/reel/video/p0l39967/watch) [![Getty Images 1224663560](https://ichef.bbci.co.uk/images/ic/480x270/p0kzkbfc.jpg.webp) Using bubbles to remove forever chemicals from our water BBC Click visits a UK research team working on a solution to remove toxic chemicals known as PFAS from water. Science](https://www.bbc.com/reel/video/p0kyqdqb/watch) [![How sex with Neanderthals changed us forever](https://ichef.bbci.co.uk/images/ic/480x270/p0kytt3p.jpg.webp) How sex with Neanderthals changed us forever According to biologists, modern humans and Neanderthals shouldn't have been able to breed. But they did. Science](https://www.bbc.com/reel/video/p0kytlx7/watch) [![Theory of Evolution: How did Charles Darwin come up with it?](https://ichef.bbci.co.uk/images/ic/480x270/p0kqp90m.jpg.webp) Theory of Evolution: How did Charles Darwin come up with it? The British naturalist embarked on an extraordinary journey, did hundreds of experiments, and wrote for 20 years. Science](https://www.bbc.com/reel/video/p0kqkmz3/watch) [!['Homo juluensis': Possible new ancient human identified](https://ichef.bbci.co.uk/images/ic/480x270/p0kgwsjn.jpg.webp) Homo juluensis: Possible 'new ancient human' identified Researchers may have identified a new human species that lived around 300,000 years ago in Asia. Science](https://www.bbc.com/reel/video/p0kftjyg/watch) [![How Arctic communities protect themselves from avalanches](https://ichef.bbci.co.uk/images/ic/480x270/p0kfy5cr.jpg.webp) How Arctic communities protect themselves from avalanches BBC Click finds out how local communities in Svalbard use technology to combat avalanches and heavy snowfall. Science](https://www.bbc.com/reel/video/p0kcpnm6/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![How space changed my body](https://ichef.bbci.co.uk/images/ic/480x270/p0j1h2b6.jpg.webp) Astronaut Peggy Whitson: How space changed my body Peggy Whitson has spent 675 days in space, more than any other American. Here's how it affected her body. Space](https://www.bbc.com/reel/video/p0hxbksd/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Jupiter stuns in new Juno pictures](https://ichef.bbci.co.uk/images/ic/480x270/p0k6xjz9.jpg.webp) See Nasa's spectacular new images of Jupiter The photos created by citizen scientists using Nasa's data have contributed to new discoveries about Jupiter. Space](https://www.bbc.com/reel/video/p0k6x7q8/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Why our planet's crust has tides too](https://ichef.bbci.co.uk/images/ic/480x270/p0jt9gtk.jpg.webp) Earth tides: Why our planet's crust has tides too How do they differ from the ocean? A geophysicist breaks it down for us. Weather & science](https://www.bbc.com/reel/video/p0jt8x5z/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Is Earth getting a 'mini moon' this fall?](https://ichef.bbci.co.uk/images/ic/480x270/p0jssrtv.jpg.webp) The science behind the 'mini moon' entering Earth's orbit An asteroid is going to circle our planet for two months this autumn before going on its way. Weather & science](https://www.bbc.com/reel/video/p0jsl446/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Screenshot 2024 08 22 at 8 51 13 PM](https://ichef.bbci.co.uk/images/ic/480x270/p0jp0p4j.png.webp) New Nasa sonifications: Listen to the sound of the Universe Nasa has released new 'sonifications' of the Universe on the 25th anniversary of Chandra, its X-ray Observatory. Space](https://www.bbc.com/reel/video/p0jlbpl3/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Uncovering the sunken relics of an ancient city](https://ichef.bbci.co.uk/images/ic/480x270/p0jnbpvk.jpg.webp) Uncovering the sunken relics of an ancient city Bettany Hughes goes underwater in search of ancient archaeological finds in historic Sozopol, Bulgaria. Archaeology](https://www.bbc.com/reel/video/p0jnbll0/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Screenshot 2024 08 20 at 2 00 51 PM min](https://ichef.bbci.co.uk/images/ic/480x270/p0jklf59.png.webp) In Australia, sea lions help researchers map the ocean floor Researchers in Australia put cameras on sea lions' backs to help them map the elusive ocean floor. Earth](https://www.bbc.com/reel/video/p0jkkyc6/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![The scientists drilling into an anctive Icelandic volcano](https://ichef.bbci.co.uk/images/ic/480x270/p0jhk026.jpg.webp) The scientists drilling into an active Icelandic volcano Scientists are preparing to drill into the rock of an Icelandic volcano to learn more about how volcanoes behave. Climate solutions](https://www.bbc.com/reel/video/p0jgsff2/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![Why we may have misunderstood the Universe](https://ichef.bbci.co.uk/images/ic/480x270/p0j882d0.jpg.webp) Why we may have misunderstood the Universe Research by a Nobel Prize winning astrophysicist suggests we have been wrong about the expansion of our Universe. Science](https://www.bbc.com/reel/video/p0j83nwv/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![What living in space could look like](https://ichef.bbci.co.uk/images/ic/480x270/p0hxt8vj.jpg.webp) Are inflatable habitats the future of life in space? As the reality of civilian space travel closes-in, engineers explore inflatable habitats. Space](https://www.bbc.com/reel/video/p0hxszh2/watch) [![](https://static.files.bbci.co.uk/bbcdotcom/web/20260309-121341-5f81352518-web-2.41.1-2/grey-placeholder.png)![A rare star explosion is coming](https://ichef.bbci.co.uk/images/ic/480x270/p0hvnlp0.jpg.webp) We're about to witness a once-in-a-lifetime star explosion An extremely rare stellar explosion is about to happen and we will be able to witness it with the naked eye. Space](https://www.bbc.com/reel/video/p0hvn69l/watch) * More from the BBC [9 hrs ago ![A bus in Nepal picks its way along a road on a hillside that is crumbling away beneath the road (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480x270/p0n8cpg6.jpg.webp) When the Earth moves, AI can spot it Sudden and unexpected, landslides and avalanches claim thousands of lives each year and cause billions of dollars in damage. What if we could see them coming? 9 hrs ago](https://www.bbc.com/future/article/20260323-the-ai-that-warns-people-about-landslides-and-avalanches) [1 day ago ![A Sumerian tablet from around 3200BC some of the earliest known mathematical exercises (Credit: Cuneiform Digital Library Initiative)](https://ichef.bbci.co.uk/images/ic/480x270/p0n7xpgv.jpg.webp) The ancient reason there are 60 minutes in an hour A mysterious 5,000-year-old decision led directly to how we still count time today. 1 day ago](https://www.bbc.com/future/article/20260320-the-ancient-reason-there-are-60-minutes-in-an-hour-and-60-seconds-in-a-minute) [3 days ago ![A close up of a woman's mouth as she places a nut between her teeth (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480x270/p0n7vsfj.jpg.webp) Don't count calories. Try eating smarter instead The time of day you have a meal, how fast you scoff your food and even how much you chew it can affect how many calories you get from it. 3 days ago](https://www.bbc.com/future/article/20260320-counting-calories-doesnt-work-try-eating-smarter-instead) [5 days ago ![A mother holding a child on her lap as he eats breakfast and she writes on a paper (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480x270/p0n7f73g.jpg.webp) Feeling drained? Blame these forms of hidden work Women are still taking on most of the cognitive burden of running a household. Understanding why is the key to reducing burnout. 5 days ago](https://www.bbc.com/future/article/20260318-eight-types-of-mental-load-that-leave-women-drained) [15 Mar 2026 ![A man in a blue checked shirt touching bellies with a pregnant woman in a grey dress (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480x270/p0n6jgft.jpg.webp) This baffling syndrome makes fathers feel pregnant Couvade syndrome is changing how scientists think about the role of men in childbearing. 15 Mar 2026](https://www.bbc.com/future/article/20260313-the-mysteries-of-couvade-syndrome) * - [Home](https://www.bbc.com/) - [News](https://www.bbc.com/news) - [Sport](https://www.bbc.com/sport) - [Business](https://www.bbc.com/business) - [Technology](https://www.bbc.com/technology) - [Health](https://www.bbc.com/health) - [Culture](https://www.bbc.com/culture) - [Arts](https://www.bbc.com/arts) - [Travel](https://www.bbc.com/travel) - [Earth](https://www.bbc.com/future-planet) - [Audio](https://www.bbc.com/audio) - [Video](https://www.bbc.com/video) - [Live](https://www.bbc.com/live) - [Weather](https://www.bbc.com/weather) - [BBC Shop](https://shop.bbc.com/) - [BritBox](https://www.britbox.com/?utm_source=bbc.com&utm_medium=referral&utm_campaign=footer) BBC in other languages ### The BBC is in multiple languages #### Read the BBC In your own language [Oduu Afaan Oromootiin](https://www.bbc.com/afaanoromoo) [Amharic ዜና በአማርኛ](https://www.bbc.com/amharic) [Arabic عربي](https://www.bbc.com/arabic) [Azeri AZƏRBAYCAN](https://www.bbc.com/azeri) [Bangla বাংলা](https://www.bbc.com/bengali) [Burmese မြန်မာ](https://www.bbc.com/burmese) [Chinese 中文网](https://www.bbc.com/zhongwen/simp) [Dari دری](https://www.bbc.com/dari) [French AFRIQUE](https://www.bbc.com/afrique) [Hausa HAUSA](https://www.bbc.com/hausa) [Hindi हिन्दी](https://www.bbc.com/hindi) [Gaelic NAIDHEACHDAN](https://www.bbc.com/naidheachdan) [Gujarati ગુજરાતીમાં સમાચાર](https://www.bbc.com/gujarati) [Igbo AKỤKỌ N’IGBO](https://www.bbc.com/igbo) [Indonesian INDONESIA](https://www.bbc.com/indonesia) [Japanese 日本語](https://www.bbc.com/japanese) [Kinyarwanda GAHUZA](https://www.bbc.com/gahuza) [Kirundi KIRUNDI](https://www.bbc.com/gahuza) [Korean 한국어](https://www.bbc.com/korean) [Kyrgyz Кыргыз](https://www.bbc.com/kyrgyz) [Marathi मराठी](https://www.bbc.com/marathi) [Nepali नेपाली](https://www.bbc.com/nepali) [Noticias para hispanoparlantes](https://www.bbc.com/mundo) [Pashto پښتو](https://www.bbc.com/pashto) [Persian فارسی](https://www.bbc.com/persian) [Pidgin](https://www.bbc.com/pidgin) [Polish PO POLSKU](https://www.bbc.com/polska) [Portuguese BRASIL](https://www.bbc.com/portuguese) [Punjabi ਪੰਜਾਬੀ ਖ਼ਬਰਾਂ](https://www.bbc.com/punjabi) [Russian НА РУССКОМ](https://www.bbc.com/russian) [Serbian NA SRPSKOM](https://www.bbc.com/serbian/lat) [Sinhala සිංහල](https://www.bbc.com/sinhala) [Somali SOMALI](https://www.bbc.com/somali) [Swahili HABARI KWA KISWAHILI](https://www.bbc.com/swahili) [Tamil தமிழில் செய்திகள்](https://www.bbc.com/tamil) [Telugu తెలుగు వార్తలు](https://www.bbc.com/telugu) [Thai ข่าวภาษาไทย](https://www.bbc.com/thai) [Tigrinya ዜና ብትግርኛ](https://www.bbc.com/tigrinya) [Turkish TÜRKÇE](https://www.bbc.com/turkce) [Ukrainian УКРАЇНСЬКA](https://www.bbc.com/ukrainian) [Urdu اردو](https://www.bbc.com/urdu) [Uzbek O'ZBEK](https://www.bbc.com/uzbek) [Vietnamese TIẾNG VIỆT](https://www.bbc.com/vietnamese) [Welsh NEWYDDION](https://www.bbc.com/cymrufyw) [Yoruba ÌRÒYÌN NÍ YORÙBÁ](https://www.bbc.com/yoruba) Follow BBC on: - [Terms of Use](https://www.bbc.com/pages/terms-of-use) - [Subscription Terms](https://www.bbc.com/pages/subscription-terms) - [About the BBC](https://www.bbc.co.uk/aboutthebbc) - [Privacy Policy](https://www.bbc.com/pages/privacy-policy) - [Cookies](https://www.bbc.com/usingthebbc/cookies/) - [Accessibility Help](https://www.bbc.co.uk/accessibility/) - [Contact the BBC](https://www.bbc.co.uk/contact) - [Advertise with us](https://advertising.bbcstudios.com/) - [Do not share or sell my info](https://www.bbc.com/usingthebbc/cookies/how-can-i-change-my-bbc-cookie-settings/) - [BBC.com Help & FAQs](https://help.bbc.com/hc/) - [Content Index](https://www.bbc.com/pages/content-index) - [Set Preferred Source](https://www.bbc.com/future/article/20260128-how-to-make-google-put-trusted-sources-up-top-when-you-search) Copyright 2026 BBC. All rights reserved. The BBC is not responsible for the content of external sites. [Read about our approach to external linking.**](https://www.bbc.co.uk/editorialguidelines/guidance/feeds-and-links)
Readable Markdown	25 October 2023 Jonathan O'CallaghanFeatures correspondent ![Nasa/JSC A view of the Moon orbiting the Earth taken from 3.9 million miles away by the Galileo spacecraft (Credit: Nasa/JSC)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjfr2.jpg.webp)Nasa/JSC This view of the Moon orbiting the Earth was taken by a human-built spacecraft more than 3.9 million miles away, but the nearest star is much further (Credit: Nasa/JSC) Alien astronomers might be looking in our direction from distant planets. What would they see? We've been searching the heavens for some time now. But despite decades of listening for tell-tale radio signals and hunting for signs that other worlds might be even vaguely habitable, it's been slim pickings so far. While astronomers have [identified a few possible candidates](https://iopscience.iop.org/article/10.3847/1538-4357/ac5c4e) for where life might conceivably exist elsewhere in the Universe, along with the odd [mysterious signal](https://iopscience.iop.org/article/10.3847/2515-5172/ac9408), there is yet to be any concrete evidence of alien life out there. This article is part of a week of special coverage about extraterrestrial life – all to mark the upcoming 60th Anniversary of the BBC's most famous alien lifeform, [Doctor Who](https://www.bbc.com/culture/article/20230925-time-travel-to-the-tardis-11-facts-you-need-to-know-about-doctor-who-before-watching). But what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth? That's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. "Hold the mirror up to yourself in space, and what would they see of us?" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. "We're looking. That means other worlds might be looking too." To date, we have found [more than 5,500 planets](https://exoplanets.nasa.gov/discovery/exoplanet-catalog/) orbiting other stars in our galaxy, called exoplanets. But such observations are in their infancy – [trillions of worlds are likely scattered throughout the Milky Way](https://exoplanets.nasa.gov/discovery/how-we-find-and-characterize/). Upon some of these worlds we have started to hunt both for the [chemical signatures in their atmospheres](https://exoplanets.nasa.gov/search-for-life/can-we-find-life/) that might indicate biological activity and even [technosignatures](https://www.nature.com/articles/s41550-022-01872-z) that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction. Earth has been unabashedly broadcasting its own presence into the galaxy for about a century now. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. "They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers," he says. We continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. "Radio stations don't want to broadcast into space," says Thomas Beatty, an astronomer at the University of Wisconsin in the US. "They want to broadcast to the ground." Other more modern forms of communication, like mobile phone signals, are [unlikely to be detectable](https://arxiv.org/abs/2304.13779). ![Nasa/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa/JSC)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjhl7.jpg.webp)Nasa/JSC The light pollution produced by our cities is visible from the ISS, but is likely not widespread enough to attract the attention of distant alien astronomers (Credit: Nasa/JSC) But not all of our signals are so faint. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. The furthest of these, Nasa's [Voyager 1 spacecraft](https://www.bbc.com/future/article/20170818-voyager-inside-the-worlds-greatest-space-mission), is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with. In April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might [reach other stars](https://arxiv.org/abs/2304.07400) as they wash over the remote spacecraft and continue their journey into space. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. "The signal would definitely show up as artificial," says Isaacson. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study. But what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. If they can see our planet pass in front of our Sun, [known as a transit](https://www.bbc.co.uk/news/science-environment-24642603), they could see sunlight passing through our atmosphere and pick out its different gases. In 2021, Faherty found there were [nearly 2,000 stars](https://www.nature.com/articles/s41586-021-03596-y) within 300 light-years of Earth that could potentially be able to see such a transit. "It's a good haul of worlds," she says. The best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would "be an indication of a stable liquid ocean". You might also like: - [The weird aliens of the 19th Century](https://www.bbc.com/future/article/20231019-the-weird-aliens-of-early-science-fiction) - [Are aliens real? Here's what we know](https://www.bbc.com/future/article/20231020-seven-surprising-things-we-now-know-about-aliens) - [What life might be like in oceans on other worlds](https://www.bbc.com/future/article/20190926-what-life-might-be-like-in-the-alien-oceans) [Nitrogen dioxide could also provide some clues](https://www.nasa.gov/news-release/nasa-study-to-find-an-extraterrestrial-civilization-pollution-could-be-the-solution/) that our planet was inhabited by an intelligent lifeform. The gas is "basically a byproduct of combustion", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. "So they might deduce we are burning stuff here." Chlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. "We're pretty sure they can only be produced by technology," says Macy Huston, an astronomer at the University of California, Berkeley in the US. (Read more about [how we might also be able to spot alien life from their pollution](https://www.bbc.com/future/article/20231023-could-we-find-alien-life-via-their-pollution).) By 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes One of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. In 2021, Beatty calculated that the sodium emitted from such lights [could be detectable](https://arxiv.org/abs/2105.09990) in a planet's atmosphere. "It has very sharp spectral features," says Beatty. "You'd never get that through a natural process." Earth in its current form is likely not urbanised enough to be detectable in such a way, at least within the parameters of our own telescopes. Less than [1% of the Earth's surface is covered by cities](https://essd.copernicus.org/articles/14/517/2022/). It's a long way from being an ecumenopolis – a planet-wide city, similar to the fictional world of Coruscant in the Star Wars films. If development continues at its current pace, however, by 2150 urbanisation might have swelled by 10 times its current levels, and we might then shine like a beacon to modern telescopes, says Beatty. But alien civilisations with more advanced telescopes might already be able to spot us. "It's totally feasible that there's alien astronomers that have built a 100m (330ft) space telescope that could be seeing us right now," he says. Even if alien astronomers had a smaller telescope that could only see the faint dot of our planet, they might still be able to work out it is inhabited. Knowing the tilt and rotation of Earth, the light emitted by our planet could be used to make a crude map of our surface, showing land, oceans, and even coastlines, according to Jonathan Jiang, an astrophysicist from Nasa's Jet Propulsion Laboratory in the US. "As long as you can see a point of light, you can analyse it," says Jiang, [who used a spacecraft in our Solar System](https://arxiv.org/pdf/1908.04350.pdf) in 2018 to demonstrate the technique on Earth. All of this raises the question of whether we really want to be so noticeable. "In movies we always get invaded," says Beatty. In reality, scientists are more eager to make our presence known, occasionally even sending out purposeful messages into the Universe – such as a [famous high-powered radio signal](https://www.bbc.co.uk/programmes/p053d1cx) containing a simple pictorial on humanity sent by the now-defunct Arecibo radio telescope in Puerto Rico in 1974. "I'm not really worried about Independence Day scenarios," says Beth Biller, an astronomer at the University of Edinburgh in the UK. ![Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images)](https://ichef.bbci.co.uk/images/ic/480xn/p0gnjjgj.jpg.webp)Getty Images Astronomers use radio telescopes to scan the sky for signals from space, but our own broadcasts could be picked up by similar equipment on other worlds (Credit: Getty Images) As humanity continues to alter our planet, presuming we don't end our own existence first through war or other means, Earth is likely to become more and more noticeable. Socas-Navarro says that alien astronomers could even one day spot [the cloud of satellites](https://arxiv.org/abs/1802.07723) orbiting our planet. We would need to have "a billion times what we have now, which sounds like a lot," he says. "But we went from one car to over a billion cars in a few decades." Perhaps, if we are eager to make first contact, we could do more to make ourselves noticed, such as broadcasts like the Arecibo message. So far, there have only been a [handful of further attempts](https://en.wikipedia.org/wiki/Active_SETI). "If it were just up to me, I'd be broadcasting our existence and hoping someone would answer," says Rimmer. "But that's just my opinion. This is a decision that I think should be made globally." If the public were in favour, one idea could be to build huge structures in space, says Beatty, such as a large planet-sized triangle or square made of a thin material that would be obviously artificial to alien astronomers. "That would be the main way to get noticed, if we wanted to," he says. For the time being, signs of our existence are more modest, but still detectable. "They don't need miracles," says Seth Shostak, senior astronomer at the Seti Institute (Search for Extraterrestrial Intelligence) in the US. "They just need the technology we have, but on a larger scale." The real question we should ask: is anyone looking our way to notice? \-- If you liked this story, [sign up for The Essential List newsletter](https://cloud.email.bbc.com/SignUp10_08?&at_bbc_team=studios&at_medium=Onsite&at_objective=acquisition&at_ptr_name=bbc.com&at_link_origin=featuresarticle&at_campaign=essentiallist&at_campaign_type=owned) – a handpicked selection of features, videos and can't-miss news delivered to your inbox every Friday. Join one million Future fans by liking us on [Facebook](https://www.facebook.com/BBCFuture/), or follow us on [Twitter](https://twitter.com/BBC_Future) or [Instagram](https://www.instagram.com/bbcfuture_official/).
Shard	16 (laksa)
Root Hash	1643509356818581016
Unparsed URL	com,bbc!www,/future/article/20231024-how-aliens-might-detect-our-existence-on-earth s443