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Mars holds a particular topographic point in the human imaginativeness as the planet most like the Earth. It has an ambiance, seasons, and typical polar ice caps. The ice caps, foremost observed by Giovanni Cassini in 1666, instantly raised tantalising inquiries. Are they made of H2O ice like the elephantine glaciers that clutter Antarctica? Are they the frozen remains of long-vanished oceans? If they melted, could Mars go a habitable topographic point? NASA ‘s Mars Global Surveyor, presently in orbit about the Red Planet, is eventually supplying some solid replies.

The Surveyor has already revealed unexpected inside informations about the size and construction of Mars ‘s northern cap. By the terminal of February, the ballistic capsule will get down function, for the first clip, the topography and composing of the even more ill understood southern polar ice cap. The new information ( along with approaching informations from the Mars Polar Lander, which will get in December ) will deprive off many of the lingering enigmas of the Martian poles.

On Mars, the presence of H2O — indispensable for life, yesteryear or nowadays — is ever an issue of great involvement. “ Some people have proposed that there were oceans early in Martian history ; others have said there were non. “ But for all of those theories, one needs to understand the H2O rhythm: how much H2O there was, where it went to, and where it ‘s at now. ” If scientists find significant militias of frozen H2O, it would bolster the position that Mars was one time a balmy, moist universe where life could hold started.

Until approximately two months ago, planetal uranologists believed that the southern cap contained nil but frozen C dioxide, besides known as dry ice. New research suggests otherwise: a thick sheet of C dioxide ice would be excessively soft to remain stable. “ The idea now is that C dioxide ice is so weak that it would flux off, like a glacier, even at really low temperatures, ” Zuber explains. “ So to keep the topography of the south polar cap, there has to be H2O ice in at that place stiffening it up. ”

Zuber and her co-workers besides analyzed Mars ‘s much larger northern polar cap. The ice cap is cut by deep troughs and chasms ; some of these depressions extend down over a stat mi to the base of the planet ‘s crust. Many research workers off guard. “ There are no troughs of that sort in any of the ice caps on Earth, ” said Global. “ We do n’t cognize how this formed

Zuber ‘s consequences confirmed that the northern cap is composed wholly of H2O ice, in some countries interspersed with beds of wind-blown dust and deposit. That piece of good intelligence came as no surprise, because summer temperatures at the cap ( which has an lift several stat mis lower than the southern cap ) are high plenty to zap frozen C dioxide. But the Global Surveyor besides produced the first accurate measuring of the size of the northern cap — and that was a surprise.

Seven hundred an

vitamin D 50 stat mis across, and up to two stat mis thick, the northern cap has a volume merely half that of the Greenland ice sheet. It may sound big, but does n’t incorporate about plenty H2O to account for the inundation channels and other eroding characteristics that appear all over the topographic point on Mars. “ It ‘s non even shut to what is by and large believed to hold one time been on the surface, ” says Zuber. Scientists like Michael Carr at the U.S. Geological Survey who believe oceans one time covered much of Mars face a serious challenge from the Global Surveyor surveies. The northern cap contains no more than one ten percent the sum of H2O needed to make full an ancient ocean. On the other manus, the crevices and ring of residuary ice around the margin of the cap suggest it has lost a great trade of H2O over the millenary.

The Global Surveyor has besides provided some hints about the manner H2O circulated about on Red planets in the distant yesteryear. The northern ice cap sits nestled within a deep depression that covers basically the full Northern hemisphere of Mars and beads in lift as it nears the pole. The cap “ looks something like a hockey Puck in that depression, ” David Smith of NASA ‘s Goddard Space Flight Center reported at the AGU imperativeness conference. Research workers are non certain how the elephantine lowland formed ( possibly through a big impact ) , but they do cognize that it has been there since really early in Martian history, and so has clearly played an of import function in the planet ‘s H2O rhythm.

“ Before we made these measurings of the Northern hemisphere, it used to be thought that the lone manner you could acquire H2O to the north pole of Mars was through the ambiance, ” Zuber says. But because the northern cap lies at a lower lift than the remainder of the planet, “ H2O than you put down about anyplace in the Northern hemisphere is traveling to flux toward the pole. It is rather likely, so, that you one time had standing organic structures of H2O at high northern latitudes. They might non hold persisted for really long, because we do n’t cognize how warm it was and things may hold frozen over rapidly. But you clearly could acquire the H2O up near to the pole. ”

Clearly, Mars was non ever the frozen barren it is today. What happened? Some of the ancient H2O could hold been lost to the ambiance and so, over infinite millenary, ejected into infinite through complicated interactions with the Martian magnetic field. Some might still be locked in aquifers and other formations beneath the surface. And some may be in the southern polar cap — but non much. The southern cap is significantly smaller than the northern 1. Even if the Mars Global Surveyor finds H2O ice in the South, it wo n’t come near to extinguishing the H2O deficit, harmonizing to Zuber.

“ We have n’t either improved or diminished the possibility of life on Mars, ” she says. “ Basically, what we have done is exacerbate the job of there being excessively small H2O on Mars today compared to where there was earlier. Now those people who have proposed oceans have a bigger undertaking in explicating where the H2O went. ”

— Kathy Svitil

Posted 2/19/99