Difference between revisions 794501666 and 794530674 on enwiki

[[File:Phoenix landing2.jpg|thumb|300 px|Artist's impression  of the Phoenix Lander landing on Mars.<br><br>Phoenix's atmospheric measurements of isotope ratios of carbon and oxygen gave evidence for liquid water on the surface now or in the recent geological past.<ref name=phoenixisotope/> Also its 2008 observations of possible droplets on its legs suggested new ways that water could be stable temporarily on Mars.<ref name=phoenix_droplets_2009/> These observations lead ma(contracted; show full), with respect to elevation (upper map) and surface brightness, or albedo (lower map). Recurrent slope linea are a class of markings that might be caused by flow of salty water. These dark lines advance downhill during warmer months, fade away in colder months, and reappear the following year. A paper by McEwen et al. in Nature Geoscience in December 2013 focuses on recent confirmation that these features exist surprisingly close to the equator. A cluster of recent findings is in the Valles Marineris area.
  The albedo information comes from the Thermal Emission Spectrometer on NASA's Mars Odyssey orbiter. Surface topographical information for the map comes from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter.]]

Upper map shows elevation, lower map shows albedo, and the black squares are confirmed sites of recurrent slope lineae.

{{quote|"We observe the lineae to be most active in seasons when the slopes often face the sun. Expected peak temperatures suggest that activity may not depend solely on temperature. Although the origin of the recurring slope lineae remains an open question, our observations are consistent with intermittent flow of briny water. Such an origin suggests surprisingly abundant liquid wa(contracted; show full)g it. This is a process familiar on the Earth for instance in Antarctica. On Earth, in similar conditions, the surface ice remains frozen, but a layer of liquid water forms from 0.1 to 1 meters below the surface. It forms preferentially in "blue ice".<ref>Nl, K., and T. SAND. [http://www.igsoc.org:8080/journal/42/141/igs_journal_vol42_issue141_pg271-278.pdf "Melting, runoff and the formation of frozen lakes in a mixed snow and blue-ice field in Dronning Maud Land, Antarctica."], J
  ournal oJf Glaciology, T'ol. 42, .\"0.141, 1996</ref>

On Mars, in his model, the melting layer is 5 to 10&nbsp;cm below the surface. The liquid water layer starts off millimeters thick in their model, and can develop to be centimeters thick as the season progresses. The effect of the warming is cumulative over successive sols. Once formed, the liquid layer can persist overnight. Subsurface liquid water layers like this can form with surface temperatures as low as -56&nbsp;°C.

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It is not yet clear how they formed. Sulfates, chlorides and nitrates can be made in sufficient quantities by atmospheric processes, but this mechanism doesn't seem sufficient to explain the observed abundances of perchlorates on Mars.<ref>[http://www.sciencedirect.com/science/article/pii/S0019103513005058 The formation of sulfate, nitrate and perchlorate salts in the martian atmosphere], Megan L. Smitha,
 , , Mark W. Claireb, d, David C. Catlinga, Kevin J. Zahnlec, Icarus
Volume 231, 1 March 2014, Pages 51–64</ref>

Though there is little by way of water vapour in the Mars atmosphere, which is also a near vacuum - still it reaches 100% humidity at night due to the low nighttime temperatures. This effect creates the Martian morning frosts, which were observed by Viking in the extremely dry equatorial regions of Mars.

(contracted; show full)le to tolerate them in these conditions, and some of them can use them as a source of energy as well.<ref name=Oren>[http://www.ncbi.nlm.nih.gov/pubmed/24150694 Perchlorate and halophilic prokaryotes: implications for possible halophilic life on Mars] Oren A1, Elevi Bardavid R, Mana L.. Water Sci Technol. 2009;60(7):1745-56. doi: 10.2166/wst.2009.635.</ref>

These layers are predicted to lie a few cms below the surface, and are likely to be thin films or droplets or patches of liquid brine. So,
  they probably won't be detected from orbit, at least not directly. Confirmation may have to wait until we can send landers to suitable locations with the capabilities to detect these layers. Some of the layers may form in equatorial regions, and analysis of results from Curiosity in early 2015 has returned indirect evidence for presence of subsurface deliquescing brines in Gale Crater.<ref name=Rincon/>

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You can also get similar eutonic mixtures of three or more different types of salts, which typically have even lower ERH than any of the mixtures of two salts. Salts on Mars could have a mixture of perchlorates, chlorates, sulfates, and chlorides and p
rerhaps nitrates also if present, along with cations of sodium, potassium, calcium, and magnesium. So there are many possibilities to consider here.

===After salt mixtures take up water, they retain it after supercooling, and reduced humidity===

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But so far no currently active volcanism has been observed, nor have any present day warm areas have ever been found on the surface, in extensive searches.<ref>[http://redplanet.asu.edu/?p=501 Hunting for young lava flows] Red Planet report, 
Posted on June 1, 2011
, by rburnham</ref> The Mars Global Surveyor scanned most of the surface in infrared with its TES instrument. The Mars Odyssey's THEMIS, also imaged the surface in wavelengths that measure temperature.

(contracted; show full)lorate-life-mars-phoenix/|publisher=Scientific American|date=August 5, 2008}}</ref><ref>{{cite journal|last1=Minkel|first1=JR|title=NASA Says Perchlorate Does Not Rule Out Life on Mars - Unexpected chemical in Martian soil is a food source for some Earthly microbes|journal=Scientific American|date=August 5, 2008|url=https://www.scientificamerican.com/article/perchlorate-life-mars-phoenix/}}</ref> For a modern view on them, Cassie Conley, planetary protection officer for NASA is quoted in 
t''The New York tTimes'' as saying:<ref name="nytimes.com">{{cite news|last1=CHANG|first1=KENNETH|title=Mars Is Pretty Clean. Her Job at NASA Is to Keep It That Way|url=https://www.nytimes.com/2015/10/06/science/mars-catharine-conley-nasa-planetary-protection-officer.html|date=October 5, 2015}}</ref><ref name="nytimes.com"/><ref>{{cite news|last1=Chang|first1=Kenneth|title=Mars Is Pretty Clean. Her Job at NASA Is to Keep It That Way.|url=https://www.nytimes.com/2015/10/06/science/mars-ca(contracted; show full)t;br><br>So far there is no evidence that microbes can actually grow there. It might be the only natural body of water on the Earth of any size without indigenous life. It is of great interest to scientists studying the water activity limits of habitability for astrobiology.<ref>Lyons, W. Berry, and Diane M. McKnight. [https://books.google.co.uk/books?id=6zjc-azebQYC&pg=PA183 "Life in Antarctic Deserts and other Cold Dry Environments." - Description of Don Juan pond(page 183)],
  Cambridge University Press, 29 Apr 2010  , see also [http://thecasscentre.co.uk/uk/catalogue/catalogue.asp?isbn=9780521889193&ss=exc summary of the book]</ref>]]
Honey has a low water activity level of 0.6. That's why honey doesn't spoil - you don't need to keep honey in a fridge, because its water activity level is so low that though microbes would find plenty to eat, and though there is plenty of water there in the honey, the water is not available to the microbes because of the low water activity level.

(contracted; show full)C, very low oxygen levels about a thousandth of the levels in oceans. Though it probably originates from the surface, carbon dating shows it has lived at those depths for between 3,000 and 10,000 years, and it has been suggested that this has implications for deep subsurface multi-cellular life on Mars.<ref>[http://www.nature.com/news/2011/110601/full/news.2011.342.html Subterranean worms from hell-  New species of nematode discovered more than a kilometre underground], Nadia Drake June 2011, Nature,
  doi:10.1038/news.2011.342</ref>

Most of these candidates are single cell microbes (or microbial films). The closest Mars analogue habitats on Earth such as the hyper arid core of the Atacama desert are inhabited by microbes, with no multicellular life. So even if multicellular life evolved on Mars, it seems that most life on Mars is likely to be microbial.

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* Astrobionibbler - similar idea to UREY, smaller, later development. Able to detect a single amino acid in a gram of soil.<ref name=astrobionibbler>[http://www.astrobio.net/exclusive/5325/searching-for-organics-in-a-nibble-of-soil Searching for Organics in a Nibble of Soil],
  Michael Schirber, Astrobiology Magazine (NASA), 18th February 2013</ref>
* Planetary In-situ Capillary Electrophersis - separates the organics by ionic mobility in sub millimeter capillaries. "Lab on a chip" with the fluid manipulations done within the chip itself.<ref>Willis, P. A., Stockton, A. M., Mora, M. F., Cable, M. L., Bramall, N. E., Jensen, E. C., ... & Mathies, R. A. (2012). [http://www.lpi.usra.edu/meetings/ipm2012/pdf/1038.pdf Planetary In Situ Capillary Electrophoresi(contracted; show full)ina|last17=Sánchez-Román|first17=Mónica|last18=Chong-Díaz|first18=Guillermo|last19=Gómez-Elvira|first19=Javier|title=A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars|journal=Astrobiology|volume=11|issue=10|year=2011|pages=969–996|issn=1531-1074|doi=10.1089/ast.2011.0654|pmid=22149750}}</ref> As the "Life Marker Chip" it was selected for ExoMars but later descoped.<ref>{{cite web|last1=s. M. R. Sims
  , D. C. Cullen  , M. A. Sephton  , C. Bulloch  , G. Borst  , H. Leeuwis  , A. Norfini  , J. Brucato  , N. Holm  , A. Steele, P. Ehrenfreund|title=The Life Marker Chip (LMC) instrument - Antibody-based detection of organic molecules and biomarkers in Martian samples.|website=Concepts and Approaches for Mars Exploration (2012)}}</ref>

===Direct search for DNA===

These can detect life on Mars if it is DNA based so related to Earth life. As DNA sequencers, they can sequence the entire genome of any lifeform found.

* Miniaturized DNA sequencers<ref>[http://www.zmescience.com/science/martian-dna-sequencer-aline-life-041431/ Mars Sample Return Mission? Naaah… Just Beam Back Martian DNA]</ref><ref>Biomedicine News [http://www.zmescience.com/science/martian-dna-sequencer-aline-life-041431/ Genome Hunters Go After Martian DNA]</ref><ref>[http://scitechdaily.com/researchers-design-a-dna-sequencing-microchip-for-detecting-life-on-mars/ Researchers Design a DNA Sequencing Microchip for Detecting Life on Mars] Science Tech Daily, July 9, 2013</ref><ref>[http://online.liebertpub.com/doi/abs/10.1089/ast.2012.0923 Radiation Resistance of Sequencing Chips for in situ Life Detection] Christopher E. Carr, Holli Rowedder, Clarissa S. Lui, Ilya Zlatkovsky, Chris W. Papalias, Jarie Bolander, Jason W. Myers, James Bustillo, Jonathan M. Rothberg, Maria T. Zuber, and Gary Ruvkun. Astrobiology. June 2013, 13(6)  560-569. {{DOI|10.1089/ast.2012.0923}}</ref>

===Electron microscope===
* Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM)<ref>Gaskin, J.A.; Jerman, G.; Gregory, D.; Sampson, A.R., [http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6187064&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F6178851%2F6186985%2F06187064.pdf%3Farnumber%3D6187064 Miniature Variable Pressure Scanning Electron Microscope for in-situ imaging & chemical analysis] Aerospace Conference, 2012 IEEE  , vol., no., pp.1,10, 3–10 March 2012
doi: 10.1109/AERO.2012.6187064</ref>

===Search for life directly by checking for metabolic reactions===

These can detect life even if it doesn't use any recognized form of conventional life chemistry. But requires the life to be "cultivable" in vitro when it meets appropriate conditions for growth.

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==External links==
* Three days long conference on the subject in 2013 [http://planets.ucla.edu/meetings/past-meetings/mars-habitability-2013/program/ The Present-Day Habitability of Mars 2013] under the auspices of the UCLA Institute for Planets and Exoplanets - with video archived for all the talks.

==References==
{{reflist|30em}}

[[Category:Mars]]