Possible present day habitats for life on Mars (Including potential Mars special regions): Difference between revisions

* '''''Lack of nitrogen'''''. All life on Earth requires nitrogen. Also there are theoretical reasons for expecting alien organic life to use nitrogen, as the weaker nitrogen based amide bonds are essential for the processes by which DNA is replicated. Mars, compared with Earth, has little nitrogen, either in the air or in the soil. Levels of nitrogen in the air are low, possibly too low for nitrogen fixation to be possible. But they can form in Martian conditions by non biological processes - either brought to Mars by meteorites (some carbonaceous chondrites are rich in nitrogen<ref>{{cite web|title=Meteorite with abundant nitrogen for life on Earth?|url=httphttps://www.nhmbbc.acco.uk/about-us/news/2011/march/meteoritescience-withenvironment-abundant-nitrogen-for-life-on-earth95139.html12597564|website=Natural History Museum, LondonBBC|date=March 41, 2011}}</ref>), or comets, or formed by lightning, or through atmospheric processes, or there may be ancient nitrate deposits from early Mars, amongst various possible sources.<ref>"Nitrogen is continuously dry-deposited from the atmosphere of Mars even today mainly as pernitric acid. During the Amazonian, 4.3 × 1018 g NO4 could have been deposited across the martian surface if all of the nitrate is formed through atmospheric photochemistry and persists without decomposition or any further reactions. This corresponds to a concentration of 0.3 wt.% N if it is mixed uniformly to a depth of 2 m. This prediction can be confirmed or disproved by future in situ measurements."</ref>

Life on Mars may be limited to locations with local abundance of nitrates. Or, it may also be able to take advantage of fixation of nitrogen in monolayers of water, a process that can happen in present-day Mars conditions, and may be able to produce enough nitrates to supply a subsurface biosphere.<ref name="BoxeHand2012">{{cite journal|url=httphttps://yly-macauthors.gpslibrary.caltech.edu/Reprintsyly30213/A_RecentPapers1/Boxe%20et%20al%202012Boxe2012p17592Int_J_Astrobiol.pdf|last1=Boxe|first1=C.S.|last2=Hand|first2=K.P.|last3=Nealson|first3=K.H.|last4=Yung|first4=Y.L.|last5=Saiz-Lopez|first5=A.|title=An active nitrogen cycle on Mars sufficient to support a subsurface biosphere|journal=International Journal of Astrobiology|volume=11|issue=2|year=2012|pages=109–115|issn=1473-5504|doi=10.1017/S1473550411000401|bibcode=2012IJAsB..11..109B}}</ref>

| organics: meteoritic likely to be present at surface || NO{{su|b=3|p=−}}: presence or abundance unknown

A candidate metabolism would use one of the electron donors in the first column paired with one of the electron acceptors on the right as a source of energy. (The finalpaper dashalso onmentions leftCO₂ hand sidewhich is thereused justas becausean theelectron listacceptor ofby electronmethanogens donorswith ismolecular shorterhydrogen thanas the listdonor. of electron acceptors).