Prominent gullies on Mars may be the result of the melting of snow, not sub-surface ice, according to a new analysis. Images may even show remnants of the snowfield in some places, US geologist Philip Christensen suggests.
If confirmed, the idea would have important implications for the chances of finding life on Mars, as well finding water sources for any astronauts who visit the red planet in the future.
Gullies several hundred of metres wide, tens of metres deep and several kilometres long are found running down the side of ridges at latitudes between 30掳 and 70掳.
Advertisement
快猫短视频s have previously suggested the gullies were formed as ice within rock melted during warmer periods. But the persistent cold temperatures at these latitudes make this seem unlikely. Also, water would not be expected to sit in the rock on the top of ridges.
Christensen, at Arizona State University, now suggests that snow, blown periodically from the Martian poles, provides a better explanation. His model envisages that the layers of snow absorb sunlight, with a 鈥渂lanket鈥� effect allowing lower layers to melt even at sub-freezing temperatures.
Meltwater produced in this way could form a gully in about 5000 years, he estimates. He also suggest that some images show gully areas on cold, pole-facing slopes which have retained part of their snow cover, although this is covered with dust.
Living conditions
鈥淚f the snow-mantle idea is true, then it has a couple of exciting implications,鈥� Louise Bishop at University College London told 快猫短视频. 鈥淚f conditions occur under the snow mantle that allow liquid water to remain stable for a relatively long period of time, then presumably they will be suitable to sustain any microbes that may be around.鈥�
Snow mantles would shield microbes from the Sun鈥檚 harmful ultraviolet rays, Bishop says. And water deposited in this way would also be easier for future human missions to Mars to access than if it were found frozen beneath the planet鈥檚 surface.
There are three landers heading for Mars in 2003, but they are unlikely to resolve the issue. The European Space Agency鈥檚 Beagle 2 lander will touch down between 5掳 and 20掳 north 鈥� too near the equator. The target site of the two NASA landers is yet to be decided but, like the ESA mission, it is very unlikely that a mountainous region will be chosen.
In May 2002, massive fields of ice were detected near to both Mars鈥� poles by NASA鈥檚 Mars Odyssey spacecraft. The chemical signature of hydrogen was detected by the spacecraft鈥檚 gamma ray spectrometer, most probably indicating water ice.
Journal reference: Nature (DOI: 10.1038/nature01346)