Proceedings of the National Academy of Sciences<\/em><\/a>, the study examines a variety of non-biological sources of methane and assesses their potential to maintain a methane-rich atmosphere. These include volcanoes; reactions in settings such as mid-ocean ridges, hydrothermal vents, and tectonic subduction zones; and comet or asteroid impacts.<\/p>\nThe case for methane as a biosignature stems from its instability in the atmosphere. Because photochemical reactions destroy atmospheric methane, it must be steadily replenished to maintain high levels.<\/p>\n
\u201cIf you detect a lot of methane on a rocky planet, you typically need a massive source to explain that,\u201d said coauthor Joshua Krissansen-Totton, a Sagan Fellow at UCSC. \u201cWe know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically.\u201d<\/p>\n
Nonbiological sources, however, would not be able to produce that much methane without also generating observable clues to its origins. Outgassing from volcanoes, for example, would add both methane and carbon monoxide to the atmosphere, while biological activity tends to readily consume carbon monoxide. The researchers found that nonbiological processes cannot easily produce habitable planet atmospheres rich in both methane and carbon dioxide and with little to no carbon monoxide.<\/p>\n
The study emphasizes the need to consider the full planetary context in evaluating potential biosignatures. The researchers concluded that, for a rocky planet orbiting a sun-like star, atmospheric methane is more likely to be considered a strong indication of life if the atmosphere also has carbon dioxide, methane is more abundant than carbon monoxide, and extremely water-rich planetary compositions can be ruled out.<\/p>\n
\u201cOne molecule is not going to give you the answer\u2014you have to take into account the planet\u2019s full context,\u201d Thompson said. \u201cMethane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it\u2019s interacting with its star, and the many processes that can affect a planet\u2019s atmosphere on geologic timescales.\u201d<\/p>\n
The study considers a variety of possibilities for \u201cfalse positives\u201d and provides guidelines for assessing methane biosignatures.<\/p>\n
\u201cThere are two things that could go wrong\u2014you could misinterpret something as a biosignature and get a false positive, or you could overlook something that\u2019s a real biosignature,\u201d Krissansen-Totton said. \u201cWith this paper, we wanted to develop a framework to help avoid both of those potential errors with methane.\u201d<\/p>\n
He added that there is still a lot of work to be done to fully understand any future methane detections. \u201cThis study is focused on the most obvious false positives for methane as a biosignature,\u201d he said. \u201cThe atmospheres of rocky exoplanets are probably going to surprise us, and we will need to be cautious in our interpretations. Future work should try to anticipate and quantify more unusual mechanisms for nonbiological methane production.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
If life is abundant in the universe, atmospheric methane may be the first sign of life beyond Earth detectable by astronomers. Although nonbiological processes can generate methane, a new study by scientists at UC Santa Cruz establishes a set of circumstances in which a persuasive case could be made for biological activity as the source…<\/p>\n","protected":false},"author":71,"featured_media":8360,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"fifu_image_url":"https:\/\/www.rochester.edu\/newscenter\/wp-content\/uploads\/2020\/06\/fea-nasa-technosignature-frank-1.jpg","fifu_image_alt":"Methane Could Be the First Detectable Indication of Life Beyond Earth","footnotes":""},"categories":[216],"tags":[],"class_list":["post-8358","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-discovery"],"_links":{"self":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8358","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/users\/71"}],"replies":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8358"}],"version-history":[{"count":1,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8358\/revisions"}],"predecessor-version":[{"id":8359,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/8358\/revisions\/8359"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/media\/8360"}],"wp:attachment":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8358"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8358"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8358"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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