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 Although the source and the chemistry of the water is unknown, the
discovery will change scientists' thinking about whether the planet
that is most like Earth in the solar system hosts microbial life
beneath its radiation-blasted crust.
"It suggests that it would be possible for life to be on Mars
today," John Grunsfeld, NASA's associate administrator for science,
told reporters, discussing the study published in the journal Nature
Geoscience.
"Mars is not the dry, arid planet that we thought of in the past.
Under certain circumstances, liquid water has been found on Mars,"
said Jim Green, the agency's director of planetary science.
But NASA will not be rushing out to search the newly discovered
saltwater residue for life just yet.
"If I were a microbe on Mars, I would probably not live near one of
these (sites). I would want to live further north or south, quite
far under the surface and where there's more of a freshwater
glacier. We only suspect those places exist and we have some
scientific evidence that they do," Grunsfeld said.
 The discovery of the water flows was made when scientists developed
a new technique to analyze chemical maps of the surface of Mars
obtained by NASA's Mars Reconnaissance Orbiter spacecraft.
They found telltale fingerprints of salts that form only in the
presence of water in narrow channels cut into cliff walls throughout
the planet's equatorial region.
The slopes, first reported in 2011, appear during the warm summer
months on Mars, then vanish when the temperatures drop. The chemical
fingerprints of hydrated minerals did likewise, the new study
showed.
Scientists suspected the streaks, known as recurring slope lineae,
or RSL, were cut by flowing water, but previously had been unable to
make the measurements.
"I thought there was no hope," Lujendra Ojha, a graduate student at
Georgia Institute of Technology and lead author of the scientific
paper, told Reuters.
Mars Reconnaissance Orbiter makes its measurements during the
hottest part of the Martian day, so scientists believed any traces
of water, or fingerprints from hydrated minerals, would have
evaporated.
Also, the chemical-sensing instrument on the orbiting spacecraft
cannot home in on details as small as the narrow streaks, which
typically are less than 16 feet (5 meters) wide.
But Ojha and colleagues created a computer program that could
scrutinize individual pixels. That data was then correlated with
high-resolution images of the streaks. Scientists concentrated on
the widest streaks and came up with a 100 percent match between
their locations and detections of hydrated salts.
The discovery "confirms that water is playing a role in these
features," said planetary scientist Alfred McEwen, with the
University of Arizona.
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FROM WATER TO SUPPORTING LIFE?
Still unknown is whether minerals are absorbing water vapor directly
from Mars' thin atmosphere, or if there is a source of melting ice
beneath the surface.
Whatever the water's source, the prospect of liquid water, even
seasonally, raises the intriguing prospect that Mars, which is
presumed to be a cold and dead planet, could support life today.
However, McEwen said much more information about the water's
chemistry would be needed before scientists could make that
assessment.
"It's not necessarily habitable just because it's water – at least
to terrestrial organisms," he said.
The prospect of water, even extremely briny and chemically
laced-water, also has implications for future human missions to
Mars. NASA’s goal is to land U.S. astronauts on Mars in the
mid-2030s.
"Mars has resources that are useful to future travelers," Grunsfeld
said. "The water is really crucial because we need water to drink,
oxygen to breathe."
Water also can be split into its component hydrogen and oxygen
molecules to produce rocket fuel, needed to fly crews back to Earth.
The evidence that there was water on the planet as recently as last
summer and during several previous seasons was the key finding in
the study released on Monday. NASA's ongoing Mars rover Curiosity
has already found evidence that Mars had all the ingredients and
suitable habitats for microbial life to exist at some point in its
past.
Scientists have been trying to figure out how Mars transformed from
a warm, wet and likely Earth-like planet early in its history into
the cold, dry desert that exists today.
Billions of years ago, Mars, which lacks a protective, global
magnetic field, lost much of its atmosphere. Several initiatives are
underway to determine how much of the planet’s water was stripped
away and how much remains locked in ice in underground reservoirs.
(Reporting by Irene Klotz; Editing by Frances Kerry and Tom Brown)
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