Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov

RELEASE: 07-207

NASA ORBITER FINDS POSSIBLE CAVE SKYLIGHTS ON MARS

PASADENA, Calif. -- NASA's Mars Odyssey spacecraft has discovered
entrances to seven possible caves on the slopes of a Martian volcano.
The find is fueling interest in potential underground habitats and
sparking searches for caverns elsewhere on the Red Planet.

Very dark, nearly circular features ranging in diameter from about 328
to 820 feet puzzled researchers who found them in images taken by
NASA's Mars Odyssey and Mars Global Surveyor orbiters. Using Mars
Odyssey's infrared camera to check the daytime and nighttime
temperatures of the circles, scientists concluded that they could be
windows into underground spaces.

Evidence that the holes may be openings to cavernous spaces comes from
the temperature differences detected from infrared images taken in
the afternoon and in the pre-dawn morning. From day to night,
temperatures of the holes change only about one-third as much as the
change in temperature of surrounding ground surface.

"They are cooler than the surrounding surface in the day and warmer at
night," said Glen Cushing of the U.S. Geological Survey's
Astrogeology Team and of Northern Arizona University, Flagstaff,
Ariz. "Their thermal behavior is not as steady as large caves on
Earth that often maintain a fairly constant temperature, but it is
consistent with these being deep holes in the ground."

A report of the discovery of the possible cave skylights by Cushing
and his co-authors was published online recently by the journal
Geophysical Research Letters.

"Whether these are just deep vertical shafts or openings into spacious
caverns, they are entries to the subsurface of Mars," said co-author
Tim Titus of the U.S. Geological Survey in Flagstaff. "Somewhere on
Mars, caves might provide a protected niche for past or current life,
or shelter for humans in the future."

The discovered holes, dubbed "Seven Sisters," are at some of the
highest altitudes on the planet, on a volcano named Arsia Mons near
Mars' tallest mountain.

"These are at such extreme altitude, they are poor candidates either
for use as human habitation or for having microbial life," Cushing
said. "Even if life has ever existed on Mars, it may not have
migrated to this height."

The new report proposes that the deep holes on Arsia Mons probably
formed as underground stresses around the volcano caused spreading
and faults that opened spaces beneath the surface. Some of the holes
are in line with strings of bowl-shaped pits where surface material
has apparently collapsed to fill the gap created by a linear fault.

The observations have prompted researchers using Mars Odyssey and
NASA's newer Mars Reconnaissance Orbiter to examine the Seven
Sisters. The goal is to find other openings to underground spaces at
lower elevations that are more accessible to future missions to Mars.


"The key to finding these was looking for temperature anomalies at
night -- warm spots," said Phil Christensen of Arizona State
University, Tempe, principal investigator for the Thermal Emission
Imaging System on Mars Odyssey. That instrument produced both
visible-light and infrared images researchers used for examining the
possible caves.

"No other instrument at Mars could give the thermal information
crucial to this research," said the project scientist for Mars
Odyssey, Jeffrey Plaut of NASA's Jet Propulsion Laboratory, Pasadena,
Calif. "This is a great example of the exciting discoveries Odyssey
continues to make." Mars Odyssey reached Mars in 2001, years before
any of the other spacecraft currently examining the planet. Its
predecessor, Mars Global Surveyor, ended its mission last year.

The Jet Propulsion Laboratory manages Mars Odyssey and Mars
Reconnaissance Orbiter for the NASA Science Mission Directorate,
Washington. Arizona State University operates the Mars Odyssey's
Thermal Emission Imaging System. For additional information about
Mars Odyssey and the new findings, visit:

http://www.nasa.gov/mission_pages/odyssey