NASA's Mars Reconnaissance Orbiter (MRO) has detected deposits of
glass within impact craters on Mars. Though formed in the searing
heat of a violent impact, such deposits might provide a delicate
window into the possibility of past life on the Red Planet.
During the past few years, research has shown evidence about past
life has been preserved in impact glass here on Earth. A 2014 study
led by scientist Peter Schultz of Brown University in Providence,
Rhode Island, found organic molecules and plant matter entombed in
glass formed by an impact that occurred millions of years ago in
Argentina. Schultz suggested that similar processes might preserve
signs of life on Mars, if they were present at the time of an
impact.
"The work done by Pete and others showed us that glasses are
potentially important for preserving biosignatures", Cannon said. "Knowing that, we wanted to go look for them on Mars and that's what
we did here. Before this paper, no one had been able to definitively
detect them on the surface".
Cannon and Mustard showed large glass deposits are present in
several ancient, yet well-preserved, craters on Mars. Picking out
the glassy deposits was no easy task.
To identify minerals and rock
types remotely, scientists measured the spectra of light reflected
off the planet's surface. But impact glass doesn't have a
particularly strong spectral signal.
"Glasses tend to be spectrally bland or weakly expressive, so
signature from the glass tends to be overwhelmed by the chunks of
rock mixed in with it", said Mustard. "But Kevin found a way to
tease that signal out".
In a laboratory, Cannon mixed together powders with a similar
composition of Martian rocks and fired them in an oven to form
glass. He then measured the spectral signal from that glass.
Once Mustard had the signal from the lab glass, he used an algorithm
to pick out similar signals in data from MRO's
Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), for
which he is the deputy principal investigator.
|
The technique pinpointed deposits in several Martian crater central
peaks, the craggy mounds that often form in the center of a crater
during a large impact. The fact the deposits were found on central
peaks is a good indicator that they have an impact origin.
Knowing that impact glass can preserve ancient signs of life
−
and now knowing that such deposits exist on the Martian surface
today
−
opens up a potential new strategy in the search for ancient Martian
life.
"The researchers' analysis suggests glass deposits are relatively
common impact features on Mars", said Jim Green, director of NASA's
planetary science division at the agency's headquarters in
Washington. "These areas could be targets for future exploration as
our robotic scientific explorers pave the way on the journey to Mars
with humans in the 2030s".
One of the craters containing glass, called Hargraves, is near the
Nili Fossae trough, a 400-mile-long (about 650-kilometer-long)
depression that stretches across the Martian surface. The region is
one of the landing site contenders for NASA's Mars 2020 rover, a
mission to cache soil and rock samples for possible return to Earth.
Nili Fossae trough is already of scientific interest because the
crust in the region is thought to date back to when Mars was a much
wetter planet. The region also is rife with what appear to be
ancient hydrothermal fractures, warm vents that could have provided
energy for life to thrive just beneath the surface.
"If you had an impact that dug in and sampled that subsurface
environment, it's possible that some of it might be preserved in a
glassy component", Mustard said. "That makes this a pretty
compelling place to go look around, and possibly return a sample".
MRO has been examining Mars with CRISM and five other instruments
since 2006.
"This significant new detection of impact glass illustrates how we
can continue to learn from the ongoing observations by this
long-lived mission", said Richard Zurek, MRO project scientist at
NASA's Jet Propulsion Laboratory, Pasadena, California.
|