Detecting Earth from distant star-based systems: Difference between revisions

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Revision as of 07:31, 22 October 2023

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{{use dmy dates |date=October 2020}}

{{short description|Detecting Earth as an exoplanet}}

[[File:Pale Blue Dot.png|thumb|upright=1.3|alt=Dark grey and black static with coloured vertical rays of sunlight over part of the image. A small pale blue point of light is barely visible.|[[Pale Blue Dot]], a photograph of [[Earth]] taken on February 14, 1990, by the ''[[Voyager 1]]'' [[space probe]] from a distance of approximately {{Nowrap|6 billion}} kilometers ({{nowrap|3.7 billion}} miles, 40.5 [[Astronomical unit|AU]])Seen from about 6 billion kilometers (3.7 billion miles). [[Earth]] is seen as a tiny dot within deep space: the blueish-white speck almost halfway up the rightmost band of light.]]

[[File:Dopspec-inline.gif|thumb|right|150px|[[Star]] dims due to [[Transit (astronomy)|transiting]] [[exoplanet]]]]

There are several methods currently used by astronomers to detect distant [[exoplanet]]s from [[Earth]].<ref name="NASA-2020">{{cite web |author=Staff |title=5 Ways to Find a Planet |url=https://exoplanets.nasa.gov/alien-worlds/ways-to-find-a-planet/ |date=2020 |work=[[NASA]] |accessdate=24 October 2020 }}</ref> Theoretically, some of these same methods may be used to detect the Earth as an exoplanet from distant star systems.

==History==

[[File:Dopspec-inline.gif|thumb|right|150px|[[Star]] dims due to [[Transit (astronomy)|transiting]] [[exoplanet]]]]

In June 2021, astronomers identified 1,715 stars (with likely related [[Planetary system|exoplanetary systems]]) within 326 [[light-year]]s (100 [[parsec]]s) that have a favorable positional vantage point—in relation to the Earth Transit Zone (ETZ)—of detecting [[Earth]] as an [[exoplanet]] [[Transit (astronomy)|transiting]] the [[Sun]] since the beginnings of human civilization (about 5,000 years ago); an additional 319 stars are expected to arrive at this special vantage point in the next 5,000 years.<ref name="NAT-20210623">{{cite journal |last1=Kaltenegger |first1=L. | author-link = Lisa Kaltenegger | last2=Faherty |first2=J.K.|author2-link=Jackie Faherty|title=Past, present and future stars that can see Earth as a transiting exoplanet |url=https://www.nature.com/articles/s41586-021-03596-y |date=23 June 2021 |journal=[[Nature (journal)|Nature]] |volume=594 |issue=7864 |pages=505–507 |doi=10.1038/s41586-021-03596-y |pmid=34163055 |bibcode=2021Natur.594..505K |accessdate=23 June 2021 |arxiv=2107.07936 |s2cid=235626242 }}</ref> Seven known exoplanet hosts, including [[Ross 128]], may be among these stars. [[Teegarden's Star]] and [[Trappist-1]] may be expected to see the Earth in 29 and 1,642 years, respectively. Radio waves, emitted by humans, have reached over 75 of the closest stars that were studied.<ref name="NAT-20210623" /> In June 2021, astronomers reported identifying 29 planets in [[habitable zone]]s that may be capable of observing the Earth.<ref name="TG20210623">{{cite news |last=Sample |first=Ian |title=Scientists identify 29 planets where aliens could observe Earth - Astronomers estimate 29 habitable planets are positioned to see Earth transit and intercept human broadcasts |url=https://www.theguardian.com/science/2021/jun/23/scientists-identify-29-planets-where-aliens-could-observe-earth |date=23 June 2021 |work=[[The Guardian]] |accessdate=23 June 2021 }}</ref> Earlier, in October 2020, astronomers had initially identified 508 such stars within 326 [[light-year]]s (100 [[parsec]]s) that would have a favorable positional vantage point—in relation to the Earth Transit Zone (ETZ)—of detecting Earth as an [[exoplanet]] [[Transit (astronomy)|transiting]] the Sun.<ref name="RAS-20201020">{{cite journal |last1=Kaltenegger |first1=L. |last2=Pepper |first2=J. |title=Which stars can see Earth as a transiting exoplanet? |url=https://academic.oup.com/mnrasl/article/499/1/L111/5931805 |date=20 October 2020 |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=499 |issue=1 |pages=L111–L115 |doi=10.1093/mnrasl/slaa161 |arxiv=2010.09766 |accessdate=24 October 2020 |doi-access=free }}</ref><ref name="LS-20201022">{{cite news |last=Letzer |first=Rafi |title=Aliens on 1,000 nearby stars could see us, new study suggests |url=https://www.livescience.com/aliens-spot-earth-exoplanets.html |date=22 October 2020 |work=[[Live Science]] |accessdate=24 October 2020 }}</ref><ref name="COR-20201021">{{cite news |last=Friedlander |first=Blaine |title=Smile, wave: Some exoplanets may be able to see us, too |url=https://news.cornell.edu/stories/2020/10/smile-wave-some-exoplanets-may-be-able-see-us-too |date=21 October 2020 |work=[[Cornell University]] |accessdate=24 October 2020 }}</ref><ref name="FRBS-20201022">{{cite news |last=Carter |first=Jamie |title=Are We Being Watched? There Are 509 Star Systems With A Great View Of Life On Earth, Say Scientists |url=https://www.forbes.com/sites/jamiecartereurope/2020/10/22/are-we-being-watched-there-are-509-star-systems-with-a-great-view-of-life-on-earth-say-scientists/amp/ |date=22 October 2020 |work=[[Forbes]] |accessdate=24 October 2020 }}</ref>

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Studies have suggested that radio broadcast leakage – with the program material likely not being detectable – may be a technosignature detectable at distances of up to a hundred light years with technology equivalent to the [[Square Kilometer Array]]<ref>{{cite web |title=How Far Into Space Can Radio Telescopes Hear? |url=https://www.forbes.com/sites/quora/2017/01/27/how-far-into-space-can-radio-telescopes-hear/ |website=Forbes |access-date=9 April 2021 |language=en}}</ref> if the ___location of Earth is known.<ref>{{cite journal |title=A direct communication proposal to test the Zoo Hypothesis |journal=Space Policy |date=1 November 2016 |volume=38 |pages=22–26 |doi=10.1016/j.spacepol.2016.06.001 |language=en |issn=0265-9646 |quote="While the limits of detection of Earth's radio transmissions are a subject of debate (Sullivan argues ~25 light-years, Atri et al. (2011) and Baum et al. (2011) up to 100 light years), as they largely depend on the size of the receiving antenna"|doi-access=free |last1=De Magalhães |first1=João Pedro |arxiv=1509.03652 |bibcode=2016SpPol..38...22D }}</ref><ref name="JCAP-2007">{{cite journal |last1=Loeb |first1=Avi |last2=Zaldarriaga|first2=Matias |title=Eavesdropping on radio broadcasts from galactic civilizations with upcoming observatories for redshifted 21 cm radiation |url=https://iopscience.iop.org/article/10.1088/1475-7516/2007/01/020/fulltext/ |journal=[[Journal of Cosmology and Astroparticle Physics]] |date=22 January 2007 |volume=2007 |page=020 |doi=10.1088/1475-7516/2007/01/020 |access-date=9 April 2021|arxiv=astro-ph/0610377 }}</ref><ref name="10.1007/978-94-009-9115-6_20"/> Likewise, if Earth's ___location can be and is known, it may be possible to use atmospheric analysis to detect life or favorable conditions for it on Earth via [[biosignature]]s, including [[MERMOZ|MERMOZ instruments]] that may be capable of remotely detecting living matter on Earth.<ref name="AA-2021">{{cite journal |author=Patty, C.H.L. |display-authors=et al. |title=Biosignatures of the Earth I. Airborne spectropolarimetric detection of photosynthetic life |url=https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202140845 |date=2021 |journal=[[Astronomy & Astrophysics]] |volume=A68 |page=651 |doi=10.1051/0004-6361/202140845 |accessdate=21 June 2021 |arxiv=2106.00493 |bibcode=2021A&A...651A..68P |s2cid=235265876 }}</ref><ref name="ARX-20210601">{{cite journal|author=Patty, C.H. Luca |display-authors=et al. |title=Biosignatures of the Earth |journal=Astronomy & Astrophysics |date=1 June 2021 |volume=651 |pages=A68 |doi=10.1051/0004-6361/202140845 |arxiv=2106.00493v1 |s2cid=235265876 }}</ref><ref name="STD-20210620">{{cite news |author=[[University of Bern]] |title=Scientists Use New Technology to Detect Signatures of Life Remotely |url=https://scitechdaily.com/scientists-use-new-technology-to-detect-signatures-of-life-remotely/amp/ |date=20 June 2021 |work=SciTechDaily.com |accessdate=21 June 2021 }}</ref>

== Experiments ==

In 1980s, astronomer [[Carl Sagan]] persuaded NASA to perform an experiment of detecting life and civilization on Earth using instruments of the ''[[Galileo (spacecraft)|Galileo]]'' spacecraft. It was launched in December 1990, and when it was 960 km from the planets's surface, ''Galileo'' turned its instruments to observe Earth. Sagan's paper was titled "A search for life on Earth from the Galileo spacecraft"; "high-resolution images of Australia and Antarctica obtained as Galileo flew overhead did not yield signs of civilization"; other measurements showed the presence of vegetation and detected radio transmissions.<ref>{{cite journal |last1=Witze |first1=Alexandra |title=How would we know whether there is life on Earth? This bold experiment found out |journal=Nature |date=16 October 2023 |volume=622 |issue=7983 |pages=451–452 |doi=10.1038/d41586-023-03230-z |url=https://www.nature.com/articles/d41586-023-03230-z |access-date=22 October 2023 |language=en}}</ref>

==See also==