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Global Warming--on Mars

Mars may be undergoing a period of profound climate change, according to a new study based on observations made by NASA's Mars Global Surveyor that show a dramatic loss of snow at the south pole.

It is not yet clear if a single year?s change represents a warming trend. "It's saying that the permanent cap isn't quite so permanent as we thought," says Michael Caplinger of Malin Space Science Systems.

The research into snow density, lead by David E. Smith of NASA?s Goddard Space Flight Center, confirms that both of Mars' polar regions are covered in permanent caps composed of carbon dioxide, which we call "dry ice."

Smith and his colleagues measured how the elevation of Mars' surface changes during the seasons, as ice builds up in winter and returns to the atmosphere in summer. Each ice cap grows during the winter and recedes in summer.

The weather on Mars can be strange. Smith's study found odd off-season snowfalls there. Because carbon dioxide does not like to be a liquid, it freezes directly out of the atmosphere into surface dry ice, at times producing ?snow--regardless of the season.

In one case, patches of snow disappeared during autumn in the northern hemisphere, at a time when cooler temperatures should have produced an accumulation of it. The large dust storm that cover the planet in recent months may have been responsible for this, temporarily raising global temperatures.

In another study, led by Michael C. Malin, features at the south pole were observed to retreat by up to 10 feet from one Martian year to the next. The odd shapes there -- circular pits, ridges and mounds -- were first photographed in 1999. Since then, some of them have eroded away by up to 50 percent. The pits are growing, while the ridges between them are shrinking.

Caplinger and Malin speculate that the features could have been created on Mars in a decade and may erode away completely within one to two decades. ?We know that the pits we see at the surface today are not very old, and that they will not last very long,? says Malin. This rate of erosion suggests the features are made of solid carbon dioxide, rather than water ice.

This finding is important because, without signs of water, it?s unlikely there was ever life on Mars. But there could still be water ice at the south pole. "We don't know what's underneath," says Caplinger. "You could certainly have water ice under carbon dioxide." He believes the only way to find out is to go there and drill down.

The newly observed melting could pump enough carbon dioxide in the atmosphere of Mars to increase its mass by 1 percent per decade, the scientists said. Already, the atmosphere of Mars is roughly 95 percent carbon dioxide. Caplinger says no one knows for sure what effect the extra carbon dioxide will have on the climate. "Not much," he thinks.

Many scientists think that Mars undergoes climate change. Photos of the surface suggest water may once have flowed on Mars, implying that the planet was once warmer. The ice ages on Earth show us that such change is normal.

Despite more than three decades of Mars exploration, scientists are still unsure about the climate of Mars. So far, observations of the planet have been confined to short time periods.

This will soon change--the Mars Global Surveyor will continue to study Mars, and the recently arrived Odyssey orbiter will begin observations early next year. Other satellites and surface probes are planned every couple of years over the next decade.

David A. Paige, a researcher at UCLA, says, "We're moving toward a situation where we'll have a permanent spacecraft presence on Mars."





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