Martian cavern: The image shows a possible cave opening informally called "Annie," which has a diameter about double the length of a football field. The Thermal Emission Imaging System camera on NASA's Mars Odyssey orbiter took the image and gathered data to show that the hole is cooler than surrounding surface in the afternoon and warmer than the surrounding surface at night. This is thermal behavior that would be expected from an opening into an underground space.
Credit: NASA
SYDNEY: NASA's Mars Odyssey probe has discovered entrances to seven possible caves on the slopes of a Martian volcano. The find hints at a new subterranean habitat for life and is sparking searches for caverns elsewhere on the Red Planet.
The dark, nearly circular features - ranging 150 to 200 m across - puzzled researchers who first found them in images taken by the U.S. space agency's Mars Odyssey and Mars Global Surveyor orbiters. Using Mars Odyssey's infrared camera to check the daytime and night-time temperatures of the circles, scientists have now concluded that they could be openings into underground spaces.
"Whether these are just deep vertical shafts or openings into spacious caverns, they are entries to the subsurface of Mars," said co-discoverer Tim Titus of the U.S. Geological Survey (UGS) in Flagstaff, Arizona. "Somewhere on Mars, caves might provide a protected niche for past or current life, or shelter for humans in the future."
The find is reported in the journal Geophysical Research Letters.
Temperature anomaly
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 co-author of the study Glen Cushing of the UGS and Northern Arizona University in Flagstaff. "Their thermal behaviour 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."
The discovered holes, dubbed the 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, noted Cushing. "Even if life has ever existed on Mars, it may not have migrated to this height."
However the find raises the possibility of other caves, at lower altitudes, that would be more hospitable to life.
The search is on
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 [and future caves] was looking for temperature anomalies at night - warm spots," said Phil Christensen of Arizona State University in Tempe, the 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.
Mars Odyssey reached Mars in 2001. Its ageing predecessor, Mars Global Surveyor, ended its mission last year.
with NASA
