New findings from NASA's Mars Reconnaissance Orbiter (MRO)
provide the strongest evidence yet that liquid water flows intermittently on
present-day Mars.
Using an imaging spectrometer on MRO, researchers detected
signatures of hydrated minerals on slopes where mysterious streaks are seen on
the Red Planet. These darkish streaks appear to ebb and flow over time. They
darken and appear to flow down steep slopes during warm seasons, and then fade
in cooler seasons. They appear in several locations on Mars when temperatures
are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at
colder times.
 |
| Martian slopes. Credit: NASA/JPL-Caltech/Univ. of Arizona |
"Our quest on Mars has been to 'follow the water,' in
our search for life in the universe, and now we have convincing science that
validates what we've long suspected," said John Grunsfeld, astronaut and
associate administrator of NASA's Science Mission Directorate in Washington.
"This is a significant development, as it appears to confirm that water --
albeit briny -- is flowing today on the surface of Mars."
These downhill flows, known as recurring slope lineae (RSL),
often have been described as possibly related to liquid water. The new findings
of hydrated salts on the slopes point to what that relationship may be to these
dark features. The hydrated salts would lower the freezing point of a liquid
brine, just as salt on roads here on Earth causes ice and snow to melt more
rapidly. Scientists say it's likely a shallow subsurface flow, with enough
water wicking to the surface to explain the darkening.
"We found the hydrated salts only when the seasonal
features were widest, which suggests that either the dark streaks themselves or
a process that forms them is the source of the hydration. In either case, the
detection of hydrated salts on these slopes means that water plays a vital role
in the formation of these streaks," said Lujendra Ojha of the Georgia
Institute of Technology (Georgia Tech) in Atlanta, lead author of a report on
these findings published Sept. 28 by Nature Geoscience.
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 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."
For more information visit:-
