ATOM & COSMOS
Magma could keep Martian lake liquid
Underground heat might explain pool of water buried under ice
B Y LISA GROSSMAN
If Mars conceals a lake beneath its
south polar ice cap, the planet must
also have a hidden chamber of magma
to keep the water liquid, a new analysis
Signs of a 20-kilometer-wide lake,
buried beneath about a kilometer and
a half of ice near Mars’ south pole, were
first reported in 2018 by a team led
by planetary scientist Roberto Orosei
(SN: 8/18/18, p. 6). The discovery kicked
off a debate over what it would take to
keep the lake liquid in such a frigid environment.
Now, planetary scientists Michael Sori
and Ali Bramson have considered various scenarios, including dust mixed in
the ice cap to improve its insulating abilities and episodes of past volcanism on
the Red Planet. The only way to create
enough heat to explain the liquid water
is if a subsurface pool of magma exists
deep beneath the lake, the pair reports
online February 12 in Geophysical
“We tried to do our due diligence and
think of all sorts of alternative factors
that could raise the temperature,” Sori
says. “The magma stuff was the only
one that did it. None of the other factors
really even came close.”
The possible lake — the first report of
so much liquid water existing on Mars
today — appeared as a bright reflection
in the radar data from the European
Space Agency’s Mars Express orbiter.
The Martian environment, though, is
too cold for water to remain liquid on
its own. Orosei, of the National Institute
of Astrophysics in Bologna, Italy, and
his colleagues had suggested that salts
dissolved in the water could keep its
melting point low, allowing the lake to
exist as a briny sludge.
Conditions beneath the ice are still
too cold, an average of –68° Celsius, to
explain the lake’s existence just with
salts, argue Sori and Bramson, both of
the University of Arizona in Tucson.
But their calculations show that if
about 300,000 years ago, a volcano
released magma into a chamber at least
5 kilometers wide and buried about
10 kilometers beneath where the lake
appears to be, that pool could generate
enough heat to still be melting salty ice
today. Without salt, the magma chamber
would have to be larger or closer to the
surface, the researchers say.
If the magma chamber is real, it would
mean that Mars has been geologically
active much more recently than plane-
tary scientists thought (SN: 3/4/17, p. 12).
Previous studies suggested that the most
recent geologic activity near Mars’ south
pole was millions of years ago, at least.
The chamber’s existence could also
potentially be a blow to the purported
lake’s habitability: If the lake is only a few
hundred thousand years old, that doesn’t
give life much time to have gotten started.
Sori and Bramson remain neutral
on whether their findings make the
lake more or less likely to exist. “
Honestly, we’re not sure,” Bramson says.
The researchers suggest that future
searches look for either the magma
chamber or the lake. So far, other radar
searches using NASA’s Mars Reconnaissance Orbiter have not spotted the lake
(SN: 12/22/18 & 1/5/19, p. 29).
The jury is out among other research-
ers, too. The new research doesn’t
rule out that salts may play a role in
melting the Mars ice, says planetary
scientist Bethany Ehlmann of Caltech,
who was not involved in either study.
But, she says, “this paper is a nice con-
tribution that explores an alternative
Orosei stands by his team’s observa-
tions. Theoretical arguments showing
how difficult it is for liquid water to be
present beneath the ice, he says, do not
prove the water is not there. “We are just
entering a long and exhausting debate,”
he says. s
Opportunity has finally run out of, well,
opportunities. After months of trying
to revive the veteran Mars rover in the
wake of a blinding dust storm, NASA has
given up on ever hearing from it again.
One last attempt to reach Opportunity
failed February 12, and NASA officials
announced the end on February 13.
But the rover will not be forgotten.
Opportunity landed on Mars in 2004
for a mission that was supposed to last
just 90 Martian days. Instead, over
15 years, Opportunity journeyed
45.16 kilometers — breaking the record
for longest rover trek on any world other
than Earth (see graph below). Along the
way, the rover found abundant evidence
that water once flowed and pooled on
the Red Planet’s surface.
What was expected to be a quick
survey of a small area “turned out to be
this overland expedition across another
planet, with mountains and valleys and
vistas and storms and sand dunes, adventure after adventure stretching on for
years,” says mission principal investigator Steve Squyres of Cornell University.
“Nobody expected that.” — Lisa Grossman
Driving distances of Mars and moon rovers
0 10 20 30 40 50
Apollo 17 rover
Apollo 15 rover
Apollo 16 rover