Mars may have more water than scientists have expected. Last month, the National Aeronautics and Space Administration (NASA) showed images that suggest liquid water has carved gullies in the planet's surface in recent times. Now, a new analysis of a Martian meteorite indicates the red planet may have lost less water to space than previously estimated.
Neither of these results is direct evidence of Martian water. In the case of water loss, Laurie Leshin at Arizona State University in Tucson looked at the ratio of two forms of hydrogen in Martian water.
Water generally consists of light water (made up of oxygen combined with light hydrogen) mixed with a small amount of heavy water (oxygen and doubly heavy hydrogen called deuterium). Martian water now has five times the concentration of deuterium as does terrestrial water, according to analyses of the Martian atmosphere. Scientists have assumed this is due to the way Mars loses its water. As solar radiation breaks up water molecules in that atmosphere, light hydrogen would more readily fly off into space than would the heavier deuterium.
Scientists thought Mars would have had to lose 90 percent of the water in its upper crust and atmosphere to produce a deuterium concentration five times higher than is found on Earth.
However, that estimate depends on the further assumption that Mars started out with water similar to Earth's primeval supply. Dr. Leshin now says that probably isn't so. She analyzed water in crystals in a meteorite found in Antarctica in 1994. Scientists believe the meteorite came from Mars. She says the meteorite crystals indicate Mars's primitive water had nearly twice the deuterium as primitive water on Earth. Her research, published in the July 15 issue of Geophysical Research Letters, says Mars should have retained up to three times more water in its crust than expected.
This conclusion enhances hopes for finding accessible liquid water on Mars - hopes already raised by the newly discovered gullies. But its main implication is to spur further research. Leshin warns that, suggestive as her work is, it does not show exactly how much water Mars actually has retained.
NASA officials likewise note that, while the 150 images from the Mars Global Surveyor spacecraft show forms of erosion not seen before on Mars, they are not proof of recent water flows. NASA will fund studies of 65,000 Global Surveyor images taken since 1997 to try to better understand what actually happened.
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