Ojha first noticed these puzzling features as a
University
of Arizona
undergraduate student in 2010, using images from the
MRO's High Resolution Imaging Science Experiment (HiRISE).
HiRISE observations now have documented RSL at dozens of
sites on Mars. The new study pairs HiRISE observations
with mineral mapping by MRO’s Compact Reconnaissance
Imaging Spectrometer for Mars (CRISM). The
spectrometer observations show signatures of hydrated
salts at multiple RSL locations, but only when the dark
features were relatively wide. When the researchers
looked at the same locations and RSL weren't as
extensive, they detected no hydrated salt.
Ojha and his co-authors interpret the spectral
signatures as caused by hydrated minerals called
perchlorates. The hydrated salts most consistent with
the chemical signatures are likely a mixture of
magnesium perchlorate, magnesium chlorate and sodium
perchlorate. Some perchlorates have been shown to keep
liquids from freezing even when conditions are as cold
as minus 94 degrees Fahrenheit (minus 70 Celsius). On
Earth, naturally produced perchlorates are concentrated
in deserts, and some types of perchlorates can be used
as rocket propellant.
Perchlorates have previously been seen on Mars. NASA's
Phoenix
lander and Curiosity rover both found them in the
planet's soil, and some scientists believe that the
Viking missions in the 1970s measured signatures of
these salts. However, this study of RSL detected
perchlorates, now in hydrated form, in different areas
than those explored by the landers. This also is the
first time perchlorates have been identified from orbit.
MRO has been examining Mars since 2006 with its six
science instruments. "The ability of MRO to
observe for multiple Mars years with a payload able to
see the fine detail of these features has enabled
findings such as these: first identifying the puzzling
seasonal streaks and now making a big step towards
explaining what they are," said Rich Zurek, MRO project
scientist at NASA's Jet Propulsion Laboratory (JPL) in
Pasadena, California.
For Ojha, the new findings are more proof that the
mysterious lines he first saw darkening Martian slopes
five years ago are, indeed, present-day water. "When
most people talk about water on Mars, they're usually
talking about ancient water or frozen water," he said.
"Now we know there’s more to the story. This is the
first spectral detection that unambiguously supports our
liquid water-formation hypotheses for RSL."
The discovery is the latest of many breakthroughs by
NASA’s Mars missions. “It took multiple spacecraft over
several years to solve this mystery, and now we know
there is liquid water on the surface of this cold,
desert planet,” said Michael Meyer, lead scientist for
NASA’s Mars Exploration Program at the agency’s
headquarters in Washington. “It seems that the more we study
Mars, the more we learn how life could be supported and
where there are resources to support life in the
future.”
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