User:Robertinventor/Modern Mars habitability
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Edited version of Draft:Present_day_habitability_of_Mars removing section on Present day Mars habitability analogue environments on Earth which already exists now as a separate article.
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One of the central questions of modern Astrobiology is whether there is, or ever has been life on Mars. Mars probably had oceans in the past, and it definitely had lakes and a thicker atmosphere. Modern Mars has become cold, dry, and almost uninhabitable, yet, if life did ever arise on Mars, some hardy microbes and perhaps even multicellular life might survive there right through to the present. The only missions to search for life on Mars, the two Viking missions, returned results that were inconclusive[3][4][5][6][7] . However the instruments were not designed to cope with the unusual conditions which Viking discovered on Mars, which may have confused the results of the experiments. Also, they didn't know enough about Mars at that time to target the regions we now think are most likely to have present day life. [8].
Life would meet many challenges on present day Mars. Liquid water boils at 0°C, over much of its surface. Even at the depths of the Hellas basin, any water is close to its boiling point of 10°C[9] and will dry out quickly. Ice also evaporates into the atmosphere over geological timescales - and most of the equatorial regions are thought to be dry to depths of tens of meters. As its axial tilt varies, Mars atmosphere is sometimes thicker, and liquid water may then form on the surface - but any dormant life in the top few meters of soil would be destroyed over periods of millions of years by cosmic radiation.
However, in 2008, droplets were observed on the landing legs of Phoenix. Sadly, there was no way to analyse them, but the leading hypothesis is that they were droplets of salty water[2]. Phoenix also made isotopic measurements which show that the Mars atmosphere has exchanged oxygen molecules with liquid on the surface in the recent geological past. This could indicate either recent episodic occurrences of liquid water (for instance after a meteorite strike) or water present every year, in contact with the atmosphere[1].
We now know of many seasonal changes in the surface of Mars which are only visible in high resolution photographs. Most of these are now thought to be caused by dry ice or wind effects. However, the "Recurrent slope lineae"[10][11][12], and some of the "flow like features" form in conditions that suggest the occasional presence of small quantities of water on Mars[13][10][14]. The evidence of flowing brines in the RSLs is strong, though it's not known if they are habitable. Curiosity has also found indirect evidence of a brine layer 15 cm below the sands that it drives over, though most scientists think that this layer is not habitable for Earth life.[15]. Recent Mars surface simulations by Nilton Renno and his team have shown that small droplets of water can form on salt / ice interfaces for a few hours per day almost anywhere on the surface of Mars, and this may explain the Phoenix leg droplets observations.[16]
In a separate development, research by the German aerospace company DLR in Mars simulation chambers and on the ISS show that some Earth life can survive simulated Mars surface conditions without any water at all, and photosynthesize and metabolize, slowly[17]. It can do this using the high relative humidity of the Mars atmosphere at night. All of this work was done after the Phoenix discoveries in 2008.
Other potential habitats include lakes formed in the higher latitudes after cometary or meteorite impacts[18], or as a result of volcanism. Covered by ice, these may remain liquid for centuries, or up to a few thousand years for the largest impacts. The planet may also have underground trapped layers of water heated by geothermal hotspots. Also there are suggestions that Mars may have a deep hydrosphere[19], a liquid layer below its cryosphere, a few kilometers below the surface. Deep rock habitats on Earth are inhabited by life so if this layer exists, it may also be habitable on Mars.
The main questions are
- Do these potential habitats exist?
- Are they habitable? For instance, liquid water, if present, could be too cold, or too salty for Earth life[15]
- Are they in fact inhabited by any forms of life? As Mars is so inhospitable, life might not be able to spread to new habitats easily. So there might be life in some of the habitats and not in others. Or life on Mars may have gone extinct, or never evolved at all, in which case none of the habitats would be inhabited.[20]
These discoveries have renewed interest in this topic, with many astrobiologists saying that they think present day Mars may be more habitable than previously thought. The first conference on the Present Day Habitability of Mars was held in 2013 in UCLA. [21][22][23]. The 2017 conference session on Modern Mars Habitability will run from April 24-28 in Mesa, Arizona [24]