Water on Mars remained billion years more than believed: NASA

Dharam Shourie

New York, Oct 29 (PTI) Liquid water remained on Mars'
surface a billion years more than scientists believed and
played an important role in shaping the planet's surface and
perhaps hosting life, new data received from the American
space agency's reconnaissance orbiter suggests.

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, the space agency, NASA, said.

"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.

"The identification of opaline silica tells us that water
may have existed as recently as two 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 three billion years ago, hydrated sulfates
formed from the evaporation of salty and sometimes acidic
water, NASA reported.

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, California.

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 colours, or wavelengths, of
reflected sunlight to detect minerals on the surface of Mars.
Its highest resolution is 20 times sharper than any previous
look at the planet in near-infrared wavelengths.