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Mars Water Search Continues, Saturn Probe Brings Surprises - 2004-08-06

Scientists looking for evidence there was once water on Mars have had mixed success. One of the two U.S. robot rovers has turned up chemical signs that a shallow salt water sea once existed on one side of the red planet, but researchers' hopes for a similar finding on the other side have been dashed so far. Yet they are not giving up. Elsewhere in the solar system, Saturn has yielded surprising findings to an orbiting U.S.-European spacecraft.

It has been seven months since the U.S. Spirit rover landed near Gusev Crater, a 160 kilometer wide ditch that scientists believe was formed by an impact from space and once held a martian lake. So far, however, they have not turned up evidence of extensive water in the crater as the twin rover "Opportunity" did on the opposite side of the planet.

The mission's main researcher, Cornell University geologist Steven Squyres, says he and his colleagues carefully chose the crater as a landing target precisely because they had hoped to find such evidence.

"It's got a dried up river valley flowing into it, so there has to have been, we think, a lake there once upon a time," he says. "The water that flowed in would have carried sediments, the sediments would have been deposited, and our initial thought was that by looking at those sediments, we could learn something about what conditions in the water were like when the lake was there. We had hoped that in driving to an impact crater, and looking down in there we might find sediments exposed there. We did not."

In papers in the journal Science, Mr. Squyres and his team report that they did find tantalizing traces of small amounts of old water at Gusev Crater. Water apparently seeped through the ground in tiny veins and deposited salt that covered rocks and cemented dust together.

He thinks his original guess about a lake is correct, but that the evidence is covered by volcanic rocks churned up when something from space smashed into the nearby surface.

"What we have concluded is that, yeah, there probably are sediments somewhere in Gusev Crater, but where we landed at least, they appear to have subsequently been buried by a fairly thick layer of this lava, so the sediments, we believe, are not accessible to us at this location," he added.

The Spirit rover is now scouring a range of hills three kilometers beyond the crater, searching for bedrock that scientists say could have been shaped by water.

The U.S. space agency, NASA, dispatched the twin rovers to seek signs of past water as part of a series of missions to determine if Mars ever had life.

The Cassini Huygens probe orbiting Saturn, has gratified researchers with several findings, including the discovery of a new radiation belt around the planet. Such belts are rings of electrically charged atomic particles that are trapped by Saturn's magnetic field. Scientists say radiation belts affect the temperature and chemistry of a planet's atmosphere, and have an impact on moons, and orbiting gas and dust. Earth has them and we have known that Saturn has them extending like elongated loops far beyond either side of the planet and its rings. But the new belt is unusual because it is inside the rings, close to the planet just above the cloud tops.

Another new finding is a glow around Saturn's biggest moon, Titan. Project scientist Dennis Matson describes it from the Jet Propulsion Laboratory in California.

"The visual and infrared mapping spectrometer obtained images of Titan that show a glowing emission due to fluorescence of methane gas. This is something that was a total surprise. It's a new discovery and it reflects the presence of methane gas at very high altitude," he says.

Finally, Cassini-Huygens has picked up crackling and popping radio signals characteristic of lightning storms. Mr. Matson says the signals are different than what the two U.S. Voyager spacecraft detected when they flew by Saturn in the early 1980s.

"We're seeing lightning in much more detail and also at higher latitudes than Voyager saw those emissions. We think that the lightning is related to storms that seem to be tracking the shadow cast by the rings in the atmosphere of Saturn," he notes.

Mr. Matson says that the difference in the lightning patterns may be because of changes in the way the ring's shadows fall on Saturn compared to the 1980s.