Posted on 02/19/2004 11:12:17 PM PST by LibWhacker
Peering into a hole that it dug, the Mars rover Opportunity has turned up new puzzles for scientists to ponder.
Since landing Jan. 25, the Opportunity has been exploring the same small crater. One intriguing feature of that crater, in the middle of the vast plain Meridiani Planum, is the small pebbles, many almost perfectly round, scattered over the surface.
The rover also saw these pebbles, about the size of BB's, embedded in an outcrop of bedrock it cruised past last week, and scientists wanted to see what lies in the dirt, too.
By holding five of its six wheels steady and then spinning its right front wheel, the Opportunity gouged a trench about a foot and a half long, six inches wide wide and four inches deep on Monday. It then spent three days examining the trench with a camera and two other instruments at the end of a mechanical arm.
"What we're seeing is spherules again," Dr. Albert Yen, a planetary scientist at NASA's Jet Propulsion Laboratory, said at a news conference yesterday. "They're not only on the top of the surface, but they're underneath as well. Now, what's interesting here is that they appear polished. They appear shiny. Not sure what's going on here."
Such round objects could be beads of glass formed from molten rock thrown up by volcanic eruptions or meteor impacts, or they could be pebbles that grew round with layers of sediment as they rolled at the bottom of shallow water.
In addition, the soil at the bottom of the trench turned out to be much more fine-grained than the surface soil. "What's underneath is what's at the immediate surface, and this trenching has exposed a region that's completely different," Dr. Yen said.
Water vapor from the atmosphere might be bringing up salt that acts as a cement to clump the fine-grained soil into the sand-size grains seen at the surface.
Another possibility, said Dr. Steven W. Squyres, the mission's principal investigator, is that finer particles at the surface had been blown away by wind.
The Opportunity will next head back to the outcrop to examine a section the scientists have nicknamed El Capitan, where a rougher-looking ledge overhangs a smoother surface. "You get a sense there are different materials here," Dr. Squyres said.
Meanwhile, on the other side of Mars, Opportunity's twin, the Spirit, will pause in the middle of its trek to a depression nicknamed Bonneville Crater to dig its own trench in the Martian soil.
The Spirit, which landed three weeks before the Opportunity and was out of operation for two almost weeks last month because of a computer flaw, has already passed the halfway point of its planned three-month mission. But managers now anticipate that the rovers will work long beyond their intended lifetimes.
"Doubling is certainly not out of the question," Richard Cook, the project manager, said Wednesday.
The Spirit will take another two weeks to travel the remaining 150 yards to Bonneville Crater, stopping along the way to examine rocks that might have been thrown out by the impact of the meteor that created it.
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