Mars may
have been wet for a billion years longer than previously thought, new water-related
opal evidence from NASA's Mars Reconnaissance Orbiter suggests. The findings
have implications for the possibility that Mars once supported life.
Scientists
have known for some time that the 4.5 billion-year-old planet once harbored
liquid water because of the many features on its surface that were likely
created by flowing water.
Hydrated,
or water-containing, mineral deposits also provide telltale signs of where and
when water
was present on ancient Mars.
Until now,
only two major groups of hydrated minerals, phyllosilicates and hydrated
sulfates, have been observed by spacecraft orbiting the red planet. (The clay-like
phyllosilicates formed more than 3.5 billion years ago where igneous rock
encountered water. Hydrated sulfates formed until about 3 billion years ago
from the evaporation of salty and sometimes acidic water.)
But a new
hydrate mineral has now entered the picture: hydrated silica, commonly known as
opal.
These
opaline silicates were detected by MRO's Compact Reconnaissance Imaging
Spectrometer for Mars (CRISM) and are the youngest of the three types of
hydrated minerals. They formed where liquid water altered materials created by
volcanic activity or meteorite impacts on the Martian surface.
"This
is an exciting discovery because it extends the time range for liquid water on
Mars, and the places where it might have supported life," said CRISM
principal investigator Scott Murchie of the Johns Hopkins Applied Physics
Laboratory in Laurel, Md. "The identification of opaline silica tells us
that water may have existed as recently as 2 billion years ago."
Some of the
opaline deposits were also associated with iron sulfates, which study team
member Ralph Milliken of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said is "the exact sort of minerals you would expect to see if you had really
acidic water."
And not
only do the deposits indicate the past presence of liquid water, but that the
water "was there long enough to alter some of the rocks," Milliken
told SPACE.com. "It wasn't an overnight process."
One
particular location where the opaline silicates were found was the large canyon
system Valles Marineris.
"We
see numerous outcrops of opal-like minerals, commonly in thin layers extending
for very long distances around the rim of Valles Marineris and sometimes within
the canyon system itself," Milliken said.
The
minerals were also recently found in Gusev Crater by NASA's Mars rover Spirit.
Another recent
study, which Milliken co-authored, looked at images of the same deposits
taken by MRO's HiRISE camera.
The new
study, detailed in the November issue of the journal Geology, reveals
that opaline silicates are widespread and occur in relatively young terrain.
"What's
important is that the longer liquid water existed on Mars, the longer the
window during which Mars may have supported life," Milliken said. "The
opaline silica deposits would be good places to explore to assess the potential
for habitability on Mars, especially in these younger terrains."
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