[meteorite-list] Russia's Phobos Sample Return Mission Will Contain Bits of Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 12 Nov 2013 10:21:01 -0800 (PST)
Message-ID: <201311121821.rACIL1Qk016892_at_zagami.jpl.nasa.gov>

http://news.brown.edu/pressreleases/2013/11/phobos

Martian moon samples will have bits of Mars
Kevin Stacey
Brown University
November 11, 2013

A Russian mission to the Martian moon Phobos, launching in 2020, would
return samples from Phobos that contain bits and pieces of Mars itself.
A new study calculates how much Martian material is on the surface of
Phobos and how deep it is likely to go.

PROVIDENCE, R.I. - A planned mission to return a sample from the Martian
moon Phobos will likely be a twofer, according to a study by Brown University
geologists.

The study helps to confirm the idea that the surface of Phobos contains
tons of dust, soil, and rock blown off the Martian surface by large projectile
impacts. Phobos? orbital path plows through occasional plumes of Martian
debris, meaning the tiny moon has been gathering Martian castoffs for
millions of years. That means a sample-return mission planned by the Russian
space agency could sample two celestial bodies for the price of one.

"The mission is scheduled to be flown early in the next decade, so the
question is not academic," said James Head, professor of geological sciences
and an author on the study. "This work shows that samples from Mars can
indeed be found in the soil of Phobos, and how their concentration might
change with depth. That will be critical in the design of the drills other
equipment."

The research appears in the latest issue of Space and Planetary Science.

The Russian mission will be the space agency's second attempt to return
a sample from Phobos. Head was a participating scientist on the first
try, which launched in 2011, but an engine failure felled the spacecraft
before it could leave Earth orbit. The next attempt is scheduled to launch
in 2020 or shortly thereafter.

This new research grew out of preparation for the original mission, which
would still be en route to Phobos had it not encountered problems. Scientists
had long assumed Phobos likely contained Martian bits, but Russian mission
planners wanted to know just how much might be there and where it might
be found. They turned to Head and Ken Ramsley, a visiting researcher in
Brown's planetary geosciences group.

To answer those questions, Ramsley and Head started with a model based
on our own Moon to estimate how much of Phobos' regolith (loose rock and
dust on the surface) would come from projectiles. They then used gravitational
and orbital data to determine what proportion of that projectile material
came from Mars.

"When an impactor hits Mars, only a certain of proportion of ejecta will
have enough velocity to reach the altitude of Phobos, and Phobos' orbital
path intersects only a certain proportion of that," Ramsley said. "So
we can crunch those numbers and find out what proportion of material on
the surface of Phobos comes from Mars."

According to those calculations, the regolith on Phobos should contain
Martian material at a rate of about 250 parts per million. The Martian
bits should be distributed fairly evenly across the surface, mostly in
the upper layers of regolith, the researchers showed.

"Only recently - in the last several 100 million years or so - has Phobos
orbited so close to Mars," Ramsley said. "In the distant past it orbited
much higher up. So that's why you're going to see probably 10 to 100 times
higher concentration in the upper regolith as opposed to deeper down."

And while 250 parts per million doesn't sound like a lot, the possibility
of returning even a little Martian material to Earth gets planetary scientists
excited. It's a nice bonus for a mission primarily aimed at learning more
about Phobos, a mysterious little rock in its own right.

Scientists are still not sure where it came from. Is it a chunk of Mars
that was knocked off by an impact early in Martian history, or is it an
asteroid snared in Mars' orbit? There are also questions about whether
its interior might hold significant amounts of water.

"Phobos has really low density," Head said. "Is that low density due to
ice in its interior or is it due to Phobos being completely fragmented,
like a loose rubble pile? We don't know."

If all goes well, the upcoming Russian mission will help solve some of
those mysteries about Phobos. And we might learn a good deal about Mars
in the process.

Editors: Brown University has a fiber link television studio available
for domestic and international live and taped interviews, and maintains
an ISDN line for radio interviews. For more information, call (401) 863-2476.
Received on Tue 12 Nov 2013 01:21:01 PM PST