Water ice is spread widely across the surface of Mars in small patches, a new study reveals. Heat-sensing equipment on an orbiting probe has detected frozen deposits at various depths by penetrating several inches into the ground.
The latest findings are the most detailed ever for the presence of ice across Mars as a whole. They are said to support the idea of a cycle of activity where ice turns to running water and then evaporates into the atmosphere.
Joshua Bandfield, of Arizona State University’s School of Earth and Space Exploration, examined data sent back to Earth by the Thermal Emission Imaging System, THEMIS, on Nasa’s Mars Odyssey spacecraft.
This camera is so sensitive that it can image detail down to 330 ft in size (around 100 meters). The results build on those from another expriment on Odyssey, the Gamma Ray Spectrometer, which mapped ice at shallow depths but could only spot those 300 miles or more wide (about 500km).
Dr Bandfield says: “We find the top layer of soil has a huge effect on the water ice in the ground.” THEMIS is a sophisticated camera that takes images in 5 visual bands and 10 heat-sensing ones. At infrared wavelengths, the smallest details THEMIS can see on the surface are 330 feet (100 meters) wide. The new results were made using infrared images of several Martian sites, each at latitudes between 60 and 70 degrees, north and south.
University colleague Professor Philip Christensen, who designed THEMIS, said: “Scientists have known for more than a decade that water is on Mars, mostly in the form of ice. What’s exciting is finding out where the ice is in detail and how it got there. We’ve reached the next level of sophistication in our questions.”
Dr Bandfield, whose paper appears this week in the journal Nature, says that dusty areas of Mars tend to insulate the ice, allowing it to survive closer to the surface. Rocky areas pump heat into the ground and so the ice lies at greater depths. He says: “These two surface materials – rock and dust – vary widely across the ground, giving underground ice a patchy distribution.”
Dr Bandfield says his results fit long-term climatic models for Mars which show that the planet has been both warmer and colder in the past, similar to glacial cycles on Earth.
He says: “The fact that ice is present near the depth of stability in the current Martian climate shows that the ground ice is responding to climate cycles.”
He adds: “The THEMIS measurements support an active water cycle on Mars such as other research has predicted.”
In August, Nasa is due to launch Phoenix, a mission designed to land at a high latitude on Mars and dig for a sample of ice to analyse.
Photo: A THEMIS scan shows ice at different depths along a strip of Mars. Red marks the deepest ice, at least 19cms, or 7.5in, below the surface. (Nasa/JPL/Arizona State University).
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