Images From MRO Indicate New Category Of Minerals
NASA's Mars Reconnaissance Orbiter has observed a new category
of minerals spread across large regions of Mars. This discovery
suggests that liquid water remained on the planet's surface a
billion years later than scientists believed, and it played an
important role in shaping the planet's surface and possibly hosting
life.
Researchers examining data from the orbiter's Compact
Reconnaissance Imaging Spectrometer for Mars have found evidence of
hydrated silica, commonly known as opal. The hydrated, or
water-containing, mineral deposits are telltale signs of where and
when water was present on ancient Mars.
"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 Scott Murchie, the spectrometer's principal
investigator at the Johns Hopkins University 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."
Until now, only two major groups of hydrated minerals,
phyllosilicates and hydrated sulfates, had been observed by
spacecraft orbiting Mars. Clay-like phyllosilicates formed more
than 3.5 billion years ago where igneous rock came into long-term
contact with water. During the next several hundred million years,
until approximately 3 billion years ago, hydrated sulfates formed
from the evaporation of salty and sometimes acidic water.
The newly discovered opaline silicates are the youngest of the
three types of hydrated minerals. They formed where liquid water
altered materials created by volcanic activity or meteorite impact
on the Martian surface. One such location noted by scientists is
the large Martian canyon system called 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,"
said Ralph Milliken of NASA's Jet Propulsion Laboratory in
Pasadena, CA.
Milliken is lead author of an article in the November issue of
"Geology" that describes the identification of opaline silica. The
study reveals that the minerals, which also were recently found in
Gusev Crater by NASA's Mars rover Spirit, are widespread and occur
in relatively young terrains.
In some locations, the orbiter's spectrometer observed opaline
silica with iron sulfate minerals, either in or around dry river
channels. This indicates the acidic water remained on the Martian
surface for an extended period of time. Milliken and his colleagues
believe that in these areas, low-temperature acidic water was
involved in forming the opal. In areas where there is no clear
evidence that the water was acidic, deposits may have formed under
a wide range of conditions.
"What's important is that the longer liquid water existed on
Mars, the longer the window during which Mars may have supported
life," says Milliken. "The opaline silica deposits would be good
places to explore to assess the potential for habitability on Mars,
especially in these younger terrains."
The spectrometer collects 544 colors, or wavelengths, of
reflected sunlight to detect minerals on the surface of Mars. Its
highest resolution is about 20 times sharper than any previous look
at the planet in near-infrared wavelengths.