Mars Odyssey Find Could Mean Underground Habitats
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 100 to 250 meters (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 US 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, CA. "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.