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This article was originally published on The conversation. The publication contributed the article to Space.com Voices of Experts: Op-Ed and Insights.
David Rothery, professor of planetary geosciences, The Open University
Venus can host life about 50km above its surface, we learned a couple of weeks ago. Now a new article, published in Nature Astronomy, reveals that the best place for life on Mars could be more than a kilometer under its surface, where an entire network of subglacial lakes has been discovered.
Mars hasn’t always been as cold and dry as it is now. There are abundant signs that water flowed across its surface in the distant past, but today you would struggle to find even any crevices you might call wet.
However, there is a lot of water on Mars today, but it’s pretty much frozen over, so it doesn’t take much for life. Even in places where the midday temperature rises above freezing, superficial marks of liquid water are frustratingly rare. This is because the atmospheric pressure on Mars is too light to confine water to a liquid state, so ice usually turns directly into vapor when heated.
Lakes under the ice
It is beginning to appear that the most favorable place for liquid water on Mars is under its vast southern polar ice cap. On Earth, such lakes began to be discovered in Antarctica in the 1970s, where nearly 400 are now known. Most of these have been detected by a “radio echo sound” (essentially radar), in which equipment on a reconnaissance plane emits radio pulses.
Some of the signal is reflected back from the surface of the ice, but some is reflected from below, especially when there is a boundary between the ice and the liquid water below. The largest subglacial lake in Antarctica is Lake Vostok – which is 240km long, 50km wide and hundreds of meters deep – located 4km below the surface.
Indications of similar lakes beneath the southern polar ice cap of Mars were first suggested by radar reflections 1.5km below the ice surface in a region called Ultimi Scopuli. These were detected between May 2012 and December 2015 by MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), an instrument carried by the European Space Agency’s Mars Express that has been orbiting the planet since 2003.
The new MARSIS data study using signal processing techniques that take into account both the intensity and sharpness (“acuity”) of reflections showed that the previously detected region actually marks the top of a liquid body. This is the Ultimi Scopuli subglacial lake and there also appear to be small patches of liquid nearby in the 250 km by 300 km area covered by the survey. The authors suggest that liquid bodies consist of hypersaline solutions, in which high concentrations of salts are dissolved in water.
They point out that calcium, magnesium, sodium, and potassium salts are known to be ubiquitous in Martian soil and that dissolved salts could help explain how subglacial lakes on Mars can remain liquid despite the low temperature at the base of the ice sheet. The weight of the overlying ice would provide the pressure needed to keep the water liquid rather than turning into steam.
Life in subglacial lakes?
Lake Vostok is advertised as a possible habitat for life that has been isolated from the Earth’s surface for millions of years and as an analog for proposed habitable environments by microbes (and possibly more complex organisms) in the inner oceans of icy moons like that of Jupiter. Europe and Saturn’s Enceladus.
Although the hypersaline water would give microbes a place to live under the southern polar ice cap of Mars, without an energy source (food) of some kind they could not survive. Chemical reactions between water and rock may release some energy but probably not enough; it would be helpful if there was an occasional volcanic eruption, or at least a hot spring, feeding into the lake.
Read more: What the hell could live in a saltwater lake on Mars? An expert explains
We lack evidence of this on Mars, unlike Europa and Enceladus. Although the new findings make Mars even more interesting than before, they have not advanced its ranking on the list of solar system bodies most likely to host life.
That said, salt water could act as a storage chamber, helping us find alien organisms that are now extinct but once arrived on Mars from other parts of the solar system.
This article was republished by The Conversation under a Creative Commons license. Read the original article.
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