water on Mars, both in the past and
present. NASA’s Mars Reconnaissance
Orbiter (MRO) confirmed that liquid
water persists on Mars’ surface
even today. It did this by studying
the composition of dark features
called recurring slope lineae, first
observed in 2010. While scientists
thought then that the flows were
signs of current liquid water on Mars,
MRO only recently confirmed in
the streaks signatures of hydrated
minerals, meaning minerals that
formed in the presence of liquid
water. These perchlorates, as they are
known, can keep water liquid even
at very cold temperatures (–94° F or
–70° C). Multiple Mars missions have
observed perchlorates, but this is the
first time they have been seen in conjunction
with the recurring slope lineae
that indicate current water. The
researchers published their results
September 28 in Nature Geoscience.
This flowing water is still a small
amount, more like dampened soil
than cascading streams. Yet in its distant
past, Mars must have streamed
with water, evidenced by the large
flood channels preserved on its
surface. Scientists are learning more
about this ancient water as well.
Researchers published September 8
in Nature Scientific Reports that contrary
to previous theories, this ancient
flooding was not the result of a
global water table coming free, but
rather regional underground frozen
deposits melting and flooding the
martian surface. And, because both
the freezing and melting processes
were regional, points out Alexis P.
Rodriguez, lead author of the study, it
is possible that large reservoirs of
water ice remain trapped under the
martian surface.
The biggest question, of course, is
why Mars lost all its water in the first
place. Astronomers know that to host
the large amounts of water the Red
Planet previously held, it must have
had a thicker atmosphere, but the
details of how it lost that atmosphere
remain vague. Researchers expected
that the martian surface should have
trapped vast stores of carbon that
used to make up the planet’s atmosphere.
But researchers published
online August 21 in Geology that far
too little carbon exists in the planet’s
carbonate minerals today to account
for the expected atmosphere of the
past. They suggest instead that Mars
lost its atmosphere upward to space
rather than hoarding it via mineral
sequestration. They also hypothesize
that the loss occurred earlier than
previously thought, so that Mars’
atmosphere was already thinning
even when rivers still flowed to form
the now-dry valleys seen on the Red
Planet today.
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