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

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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 |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 |isbn=978-0-12-446744-6 |language=en}}</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|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>

== 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 planet's surface, ''Galileo'' turned its instruments to observe Earth. Sagan's paper was titled "A search for life on Earth from the Galileo spacecraft"; he wrote that "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 |bibcode=2023Natur.622..451W |language=en |doi-access=free }}</ref><ref>{{Cite journal|url=https://www.ufrgs.br/leaa/arquivos/aulas/SERP06/1993_ASearchForLifeOnEarthFromTheGalileoSpacecraft_NATURE.pdf|title=A search for life on Earth from the Galileo spacecraft|first1=Carl|last1=Sagan|first2=W. Reid|last2=Thompson|first3=Robert|last3=Carlson|first4=Donald|last4=Gurnett|first5=Charles|last5=Hord|date=October 23, 1993|journal=Nature|volume=365|issue=6448|pages=715–721|doi=10.1038/365715a0|bibcode=1993Natur.365..715S |s2cid=4269717 }}</ref>

==See also==