NASA Spacecraft Data Suggest Water Flowing on Mars

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Guy Webster 818-354-6278
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Steve Cole 202-358-0918
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Daniel Stolte 520-626-4402
University of Arizona, Tucson
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News release: 2011-242 Aug. 4, 2011

NASA Spacecraft Data Suggest Water Flowing on Mars

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-242&cid=release_2011-242

PASADENA, Calif. -- Observations from NASA's Mars Reconnaissance Orbiter have revealed
possible flowing water during the warmest months on Mars.

"NASA's Mars Exploration Program keeps bringing us closer to determining whether the Red Planet
could harbor life in some form," NASA Administrator Charles Bolden said, "and it reaffirms Mars as
an important future destination for human exploration."

Dark, finger-like features appear and extend down some Martian slopes during late spring through
summer, fade in winter, and return during the next spring. Repeated observations have tracked the
seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars'
southern hemisphere.

"The best explanation for these observations so far is the flow of briny water," said Alfred McEwen
of the University of Arizona, Tucson. McEwen is the principal investigator for the orbiter's High
Resolution Imaging Science Experiment (HiRISE) and lead author of a report about the recurring
flows published in Thursday's edition of the journal Science.

Some aspects of the observations still puzzle researchers, but flows of liquid brine fit the features'
characteristics better than alternate hypotheses. Saltiness lowers the freezing temperature of water.
Sites with active flows get warm enough, even in the shallow subsurface, to sustain liquid water that
is about as salty as Earth's oceans, while pure water would freeze at the observed temperatures.

"These dark lineations are different from other types of features on Martian slopes," said Mars
Reconnaissance Orbiter Project Scientist Richard Zurek of NASA's Jet Propulsion Laboratory in
Pasadena, Calif. "Repeated observations show they extend ever farther downhill with time during the
warm season."

The features imaged are only about 0.5 to 5 yards or meters wide, with lengths up to hundreds of
yards. The width is much narrower than previously reported gullies on Martian slopes. However,
some of those locations display more than 1,000 individual flows. Also, while gullies are abundant on
cold, pole-facing slopes, these dark flows are on warmer, equator-facing slopes.

The images show flows lengthen and darken on rocky equator-facing slopes from late spring to early
fall. The seasonality, latitude distribution and brightness changes suggest a volatile material is
involved, but there is no direct detection of one. The settings are too warm for carbon-dioxide frost
and, at some sites, too cold for pure water. This suggests the action of brines, which have lower
freezing points. Salt deposits over much of Mars indicate brines were abundant in Mars' past. These
recent observations suggest brines still may form near the surface today in limited times and places.

When researchers checked flow-marked slopes with the orbiter's Compact Reconnaissance Imaging
Spectrometer for Mars (CRISM), no sign of water appeared. The features may quickly dry on the
surface or could be shallow subsurface flows.

"The flows are not dark because of being wet," McEwen said. "They are dark for some other reason."

A flow initiated by briny water could rearrange grains or change surface roughness in a way that
darkens the appearance. How the features brighten again when temperatures drop is harder to explain.

"It's a mystery now, but I think it's a solvable mystery with further observations and laboratory
experiments," McEwen said.

These results are the closest scientists have come to finding evidence of liquid water on the planet's
surface today. Frozen water, however has been detected near the surface in many middle to high-
latitude regions. Fresh-looking gullies suggest slope movements in geologically recent times, perhaps
aided by water. Purported droplets of brine also appeared on struts of the Phoenix Mars Lander. If
further study of the recurring dark flows supports evidence of brines, these could be the first known
Martian locations with liquid water.

The Mars Reconnaissance Orbiter is managed by JPL for NASA's Science Mission Directorate in
Washington. The University of Arizona's Lunar and Planetary Laboratory operates HiRISE. The
camera was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Johns Hopkins
University Applied Physics Laboratory in Laurel, Md., provided and operates CRISM. JPL is a
division of the California Institute of Technology in Pasadena.

For more information about the Mars Reconnaissance Orbiter, visit: http://www.nasa.gov/mro and
http://marsprogram.jpl.nasa.gov/mro/ .

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