Страница: 2/2
The Global Surveyor has also provided some clues about the way water circulated about on Mars in the distant past. The northern ice cap sits nestled within a deep depression that covers essentially the entire northern hemisphere of Mars and drops in elevation 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 press conference. Researchers are not sure how the giant lowland formed (perhaps through a large impact), but they do know that it has been there since very early in Martian history, and so has clearly played an important role in the planet's water cycle.
"Before we made these measurements of the northern hemisphere, it used to be thought that the only way you could get water to the north pole of Mars was through the atmosphere," Zuber says. But because the northern cap lies at a lower elevation than the rest of the planet, "water than you put down almost anywhere in the northern hemisphere is going to flow toward the pole. It is quite probable, then, that you once had standing bodies of water at high northern latitudes. They might not have persisted for very long, because we don't know how warm it was and things may have frozen over quickly. But you clearly could get the water up close to the pole."
Clearly, Mars was not always the frozen wasteland it is today. What happened? Some of the ancient water could have been lost to the atmosphere and then, over countless millennia, ejected into space through complicated interactions with the Martian magnetic field. Some might still be locked in aquifers and other formations beneath the surface. And some may exist in the southern polar cap--but not much. The southern cap is significantly smaller than the northern one. Even if the Mars Global Surveyor finds water ice in the south, it won't come close to eliminating the water shortage, according to Zuber.
"We haven't either improved or diminished the possibility of life on Mars," she says. "Essentially, what we have done is exacerbate the problem of there being too little water on Mars today compared to where there was earlier. Now those people who have proposed oceans have a bigger task in explaining where the water went."
--Kathy Svitil
Posted 2/19/99
Реферат опубликован: 14/06/2009