The U.S. Mars rover has dug into the red planet's soil for the first time in the U.S. space agency's quest to find traces of ancient water. Mission scientists say the day's findings reveal some surprises and pose new questions about Martian geology.
Scientists at the Jet Propulsion Laboratory in California have begun their intense scrutiny of Martian soil at the Spirit rover's landing site in Gusev Crater, which they believe is an ancient lake bed.
Cornell University researcher Stephen Squyres said his science team has probed the soil with every instrument packed onto the rover. "I have at times compared the Spirit rover to a Swiss army knife that has a whole bunch of different gadgets on it. Now for the very first time on just a little patch of soil this is the first thing that we've looked at. We have now actually brought to bear every scientific sensor that we have," he said.
Two German instruments on the rover saw signs of several iron compounds in the Martian dust as well as sulfur and chlorine. The scientists say these are not surprising, since the two U.S. Viking landers of the 1970s and the 1997 Pathfinder rover also detected them in other Martian locations.
But Mr. Squyres says he does not know yet whether this means Martian soil always had the same chemical makeup globally or one of the red planet's frequent dust storms carried this soil from a distant location.
The question could be answered when the rover starts digging deeply in a nearby crater to determine the composition of layers well below the surface.
Mr. Squyres said scientists are also puzzled by the discovery in the dust layer of an iron compound called olivine. "It is the kind of mineral that one finds in volcanic rocks, lava, basalt. It's not something that you form as a result of lots of chemical weathering. One possibility is that this Martian soil, rather than being the result of a chemical weathering process, is simply very finely ground lava. That would be a surprise to me," he said.
Finally, the Mars mission scientists are curious about what is binding the surface soil particles. They find when they tamp it down very lightly with one of the instruments, it springs back up. This suggests that the sulfur and chlorine salts in it are helping the particles stick together.
Steven Squyres said water could have transported them or volcanoes could have laid them down. "The key here, though, is we're starting to put together a comprehensive picture of what this stuff looks like. Again, this is just our first patch of dirt," he said.
The Spirit rover is likely soon to start scraping into a nearby football-sized rock it moved up to earlier in the week on its first two-meter drive away from its landing platform.
On Sunday, a twin rover is to land on the other side of Mars to begin geological studies on a flat plain.