Martian South Pole Not Just Dry Ice
Astronomers have known for years that Mars possessed polar ice caps, but early attempts at chemical analysis suggested only that the northern cap could be composed of water ice, and the southern cap was thought to be carbon dioxide ice.
Recent space missions then suggested that the southern ice cap, existing all year round, could be a mixture of water and carbon dioxide. But only with Mars Express have scientists been able to confirm directly for the first time that water ice is present at the south pole too.
Mars Express made observations with its OMEGA instrument to measure the amounts of sunlight and heat reflected from the Martian polar region. When planetary scientists analysed the data, it clearly showed that, as well as carbon dioxide ice, water ice was present too.
However, OMEGA looked at the surface with infrared eyes and, being sensitive to heat, clearly picked up the signature of water ice. The discovery hints that perhaps there are much larger quantities of water ice all over Mars than previously thought.
The second part comprises steep slopes known as scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains. The third part was unexpected and encompasses the vast permafrost fields that stretch for tens of kilometres away from the scarps.
The OMEGA observations were made between 18 January and 11 February this year, when it was late summer for the Martian southern hemisphere and temperatures would be at their highest. Even so, that is probably only -130 degrees Celsius and the ice that Mars Express has observed is a permanent feature of this location.
During the winter months, scientists expect that carbon dioxide from the atmosphere will freeze onto the poles, making them much larger and covering some of the water ice from view.
Mars Express and OMEGA will now continue looking for water ice and minerals across the surface of the planet. In May, another Mars Express instrument, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), will begin collecting data, looking for water underground. MARSIS is a radar device on the Mars Express satellite that can look through the top five kilometers of martian crust to search for layers of water and ice.
The Italian space agency is planning to fly a shallow subsurface radar, called SHARAD, on NASA's Mars Reconnaissance Orbiter to see if water ice is present at depths greater than one meter. While MARSIS has a higher penetration capability, it has much lower resolution than SHARAD will have.
"Odyssey, MER, and Mars Express will determine how much water exists at present, hopefully, and provide better constraints on past water abundance," says Jonathan Lunine of the Lunar and Planetary Laboratory at the University of Arizona,. "I am particularly interested in the MARSIS radar results, and those of its successor - SHARAD."