|water can exist as a liquid
near the Martian surface.
absorb water vapour from the atmosphere.
The results show conditions were right for the brines to form during winter
nights at the Martian equator, where Curiosity landed. But the liquid
evaporates during the Martian day when temperatures rise.
Javier Martin-Torres, a co-investigator on the Curiosity mission and lead
scientist on REMS, told BBC News the detection was indirect but convincing:
“What we see are the conditions for the formation of brines on the
surface. It’s similar to when people were discovering the first exoplanets.
“They were not seeing the planets, but they were able to see the
gravitational effects on the star.
“These perchlorate salts have a property called deliquescence. They
take the water vapour from the atmosphere and absorb it to produce the brines.”
He added: “We see a daily water cycle – which is very important. This
cycle is maintained by the brine. On Earth we have an exchange between the
atmosphere and the ground through rain. But we don’t have this on Mars.”
While one might think that liquid water would form at warmer temperatures,
the formation of brines is the result of an interaction between temperature and
atmospheric pressure. It happens that the sweet spot for formation of these
liquid films is at colder temperatures.
The fact that the scientists see evidence for these brines at the Martian
equator – where conditions are least favourable – means that they might be more
persistent at higher latitudes, in areas where the humidity is higher and
temperatures are lower.
In these regions they might even be present all year round.
Dark streaks on slopes seen by orbiting spacecraft have long been thought to
be the product of running water seeping from the Martian soil. But this
interpretation has been contested.
“It’s speculation at this point… but these observations at least
support or go in this direction,” said Dr Martin-Torres.
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