NASA probe shows how solar burps may have stripped Mars of water
The Martian weather report is in.
Information beamed back by NASA’s
MAVEN spacecraft, which has been
studying Mars’s atmosphere from orbit
since September 2014, offers a new view
of Mars’s history and could help pave the
way for crewed missions to the Red
Planet.
One of Mars’s long-standing mysteries is
what happened to its water. Geological
evidence found by NASA’s Curiosity rover
(see photograph, below) suggests the
planet was once moist enough to host
lakes and rivers , but barring a few salty
streaks we don’t see much sign of it
today.
“We’re trying to understand what changes
in the climate have occurred and what
drove them in order to go from that
warm wet planet to today’s cold, dry
more desert-like environment,” says Bruce
Jakosky of the University of Colorado,
Boulder, who heads the MAVEN mission.
To that end, MAVEN is studying how
water and other molecules could have
escaped through the planet’s atmosphere
and out into space.
Solar burp
In March this year, it watched as the sun
burped out a coronal mass ejection
(CME), a mix of gas particles and magnetic
field lines. When this mass slammed into
Mars, it generated a strong electric field in
the upper atmosphere, giving a large
number of oxygen and carbon dioxide
ions sufficient energy to escape into
space.
“The escape rate went up by a factor of
10 or 20 during that event,” says Jakosky.
The gas particles also produced a low-
altitude aurora as they entered the
atmosphere, similar to the one MAVEN
spotted last December .small-scale stripping of Martian
atmosphere could be a thin echo of the
past. It’s thought that the sun was once
more active, with a greater frequency and
intensity of CMEs. That would have
stripped even more gas out of the
atmosphere, leaving Mars barren.
Other spacecraft have seen CMEs at Mars
before, says Nicholas Heavens of Hampton
University in Virginia, but MAVEN is the
best equipped so far to measure their
effect on the atmosphere. “MAVEN is
centred on marrying observations and
models,” he says. “We’re hoping to see a
few more these events, so we get an
understanding of the diversity of CMEs.”
Deep dips
MAVEN has also performed a number of
“deep dips” into the atmosphere, lowering
the bottom of its orbit from 150
kilometres to 125 km. “That may not seem
like much, but it lets us go all the way
down to the well-mixed lower part of the
atmosphere,” says Jakosky. A dip
conducted in April revealed that the
densities of oxygen and carbon vary
across Mars, due to mixing caused by
atmospheric waves. “We’re seeing a lot of
variability that we did not expect,” he
says.
A better understanding of these densities
could help astronauts land on the surface
of Mars through a manoeuvre called
aerobreaking and aerocapture, in which
an incoming spacecraft uses a planet’s
atmosphere to safely slow down.
“If you want an efficient pathway to Mars,
these are very important things you want
to take advantage of,” says Heavens. “But
they will work best if you can accurately
model the densities you are going to
encounter in Mars’s upper atmosphere.”
Jakosky says MAVEN could also determine
whether Mars’s ionosphere is strong
enough to bounce radio waves off, letting
astronauts converse on the surface more
easily. In general he thinks the mission is
laying down a science baseline that future
missions will explore further.
He points to the opening of the recent
film The Martian, in which astronaut Mark
Watney and his crewmates are gathering
rock samples. “What they’re doing is
looking to answer the questions that we’re
helping to pose right now,” he says. “I
think Mark Watney and his fellow
astronauts would have been very familiar
with the MAVEN mission.”
