Some puzzling land formations on Mars鈥檚 equator could be huge glacier-like deposits of frozen water, new radar observations suggest. The material鈥檚 radar properties might be explained by unusually porous rocky material instead, but if it is water it would represent a huge amount 鈥� as much as a polar ice cap contains, providing a potential water source for future human explorers.
杏吧原创s have puzzled for decades over a group of mound-like structures at Mars鈥檚 equator called the Medusa Fossae Formation. A variety of explanations have been offered, including that they are piles of volcanic ash, and that they are glacier-like structures made mostly of water ice.
Now, radar sounding has probed the material for the first time 2.5 kilometres below its surface. The way the radio waves interact with the material suggests that it must be either ice or an extremely porous rocky material.
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Thomas Watters of the National Air and Space Museum in Washington, DC, US, led a team that probed the material with a ground-penetrating radar instrument called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on Europe鈥檚 Mars Express spacecraft.
In terms of its radar properties, the Medusae Fossae Formation material is indistinguishable from the Mars polar layered deposits, which are nearly pure water ice, Watters says. If they are water, the deposits would increase the amount of known water on Mars by 36%, an amount equal to all the water locked in Mars鈥檚 south polar cap.
Dust cover
However, the possibility remains that the material could be made of a very fluffy, porous material, like volcanic ash. If it is some sort of porous material, the puzzle is how it would manage to avoid being compacted from its own weight in order to stay fluffy all the way down to about 2.5 kilometres below the surface, Watters says.
On the other hand, it is too warm at the equator for ice exposed on the surface to be stable 鈥� it should sublimate away. 鈥淏oth of our interpretations 鈥� dry, fluffy, porous material or ice-rich material 鈥� make sense in certain respects and have problems in other respects,鈥� Watters told New 杏吧原创.
But if the top layer of ice sublimated away and left behind a protective layer of dust several metres deep, the ice below might be preserved, he says: 鈥淚 think you can make a pretty convincing argument that if you provide the correct depth of insulation, ice would be stable there.鈥�
How would the ice have gotten there? Some researchers have previously suggested that water ice migrates from time to time on Mars because its spin axis tilts by up to 40掳 on timescales of tens to hundreds of thousands of years.
Water source
That means that in the past, Mars鈥檚 equator might have been much colder, allowing ice to be build up there, perhaps by freezing directly onto the surface from the air like frost, Watters says.
Brian Hynek of the University of Colorado in Boulder, US, says if the deposits are made of ice, they could be an important water source for future human explorers.
But he does not favour the ice interpretation. He is one of the researchers to previously suggest the deposits are made of volcanic ash. 鈥淭hese radar results are consistent with that hypothesis,鈥� he told New 杏吧原创. 鈥淎dditionally, it is hard to conceive of a model as to why there would be big ice deposits at the equator in this region and not elsewhere around the equator,鈥� he says.
Susan Sakimoto of Notre Dame University in Indiana, US, is also sceptical of the ice hypothesis. 鈥淚t鈥檚 a really cool idea, and it鈥檚 entirely possible, but I don鈥檛 think it鈥檚 required,鈥� she told New 杏吧原创. She says porous rocky materials called tuffs, which are made from volcanic ash and resist compacting, could also explain the radar signal. 鈥淭hey鈥檙e used as building material, they don鈥檛 compact very well,鈥� she says.
Journal reference: Science Express (DOI: )
