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

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Transit method is the most popular tool used to detect exoplanets and the most common tool to [[Astronomical spectroscopy|spectroscopically]] analyze [[Extraterrestrial atmosphere#Exoplanets|exoplanetary atmospheres]].<ref name="RAS-20201020" /> As a result, such studies, based on the transit method, will be useful in the [[Extraterrestrial life|search for life on exoplanets]] beyond the [[Solar System]] by the [[Search for extraterrestrial intelligence|SETI program]], [[Breakthrough Listen|Breakthrough Listen Initiative]], as well as upcoming exoplanetary [[Transiting Exoplanet Survey Satellite|TESS mission]] searches.<ref name="RAS-20201020" />

Detectability of Earth from distant star-based systems may allow for the detectability of humanity and/or analysis of Earth from distant vantage points such as via "[[Technosignature#Atmospheric analysis|atmospheric SETI]]" for the detection of atmospheric compositions explainable only by use of (artificial) technology like [[air pollution]] containing [[Nitrogen dioxide#Human-caused sources and exposure|nitrogen dioxide]] from e.g. transportation technologies.<ref>{{cite news |title=Pollution on other planets could help us find aliens, Nasa says |url=https://www.independent.co.uk/life-style/gadgets-and-tech/alien-pollution-planets-nasa-b1801543.html |access-date=6 March 2021 | work = [[The Independent]] |date=12 February 2021 |language=en}}</ref><ref>{{cite magazine |title=Can Alien Smog Lead Us to Extraterrestrial Civilizations? |url=https://www.wired.com/story/can-alien-smog-lead-us-to-extraterrestrial-civilizations/ |access-date=6 March 2021 |magazine=Wired |language=en-us}}</ref><ref>{{cite journal |last1=Kopparapu |first1=Ravi |last2=Arney |first2=Giada |last3=Haqq-Misra |first3=Jacob |last4=Lustig-Yaeger |first4=Jacob |last5=Villanueva |first5=Geronimo |title=Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology |journal=[[The Astrophysical Journal]] |date=22 February 2021 |volume=908 |issue=2 |page=164 |doi=10.3847/1538-4357/abd7f7 |language=en |issn=1538-4357|arxiv=2102.05027|bibcode=2021ApJ...908..164K |s2cid=231855390 |doi-access=free }}</ref> The easiest or most likely artificial signals from Earth to be detectable are brief pulses transmitted by [[anti-ballistic missile]] (ABM) early-warning and space-surveillance radars during the [[Cold War]] and later astronomical and military radars.<ref>{{cite journal |title=The benefits and harm of transmitting into space |journal=Space Policy |date=1 February 2013 |volume=29 |issue=1 |pages=40–48 |doi=10.1016/j.spacepol.2012.11.006 |url=https://www.sciencedirect.com/science/article/abs/pii/S0265964612001361 |access-date=9 April 2021 |language=en |issn=0265-9646|arxiv=1207.5540 |last1=Haqq-Misra |first1=Jacob |last2=Busch |first2=Michael W. |last3=Som |first3=Sanjoy M. |last4=Baum |first4=Seth D. |bibcode=2013SpPol..29...40H |s2cid=7070311 }}</ref><ref name="10.1007/978-94-009-9115-6_20">{{cite book |last1=Sullivan |first1=W. T. III |chapter=Radio Leakage and Eavesdropping |title=Strategies for the Search for Life in the Universe |series=Astrophysics and Space Science Library |date=1980 |volume=83 |pages=227–239 |doi=10.1007/978-94-009-9115-6_20 |bibcode=1980ASSL...83..227S |isbn=978-90-277-1226-4 |chapter-url=https://ui.adsabs.harvard.edu/abs/1980ASSL...83..227S/abstract |access-date=9 April 2021}}</ref> Unlike the earliest and conventional radio- and television-broadcasting which has been claimed to be undetectable at short distances,<ref>{{cite web |title=How far from Earth could aliens detect our radio signals? |url=https://www.sciencefocus.com/space/how-far-from-earth-could-aliens-detect-our-radio-signals/ |website=BBC Science Focus Magazine |date=21 December 2019 |access-date=9 April 2021 |language=en}}</ref><ref>{{cite web |title=This is how far human radio broadcasts have reached into the galaxy |url=https://www.planetary.org/articles/3390 |website=The Planetary Society |access-date=9 April 2021 |language=en}}</ref> such signals could be detected from very distant, possibly star-based, receiver stations – any single of which would detect brief episodes of powerful pulses repeating with intervals of one Earth day – and could be used to detect both Earth as well as the presence of a radar-utilizing civilization on it.<ref>{{cite journal |title=XI. - Planets and Life around Other Stars |journal=International Geophysics |date=1 January 2004 |volume=87 |pages=592–608 |url=https://www.sciencedirect.com/science/article/pii/S0074614204800251 |access-date=5 April 2021 |publisher=Academic Press |doi=10.1016/S0074-6142(04)80025-1 |bibcode=2004InGeo..87..592. |isbn=978-0-12-446744-6 |language=en|url-access=subscription }}</ref><!--https://www.sciencedirect.com/topics/earth-and-planetary-sciences/radar-transmission-->

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 |issue=1 |page=020 |doi=10.1088/1475-7516/2007/01/020 |access-date=9 April 2021|arxiv=astro-ph/0610377 |bibcode=2007JCAP...01..020L |s2cid=119398714 }}</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 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 |access-date=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 |bibcode=2021A&A...651A..68P |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 |access-date=21 June 2021 }}</ref>