July 9, 1997 in Nation/World

An Unearthly Vision No More

David L. Chandler Boston Globe
 

Mars, already known to be the planet closest to the Earth in its surface conditions and history, is even more Earthlike than scientists had imagined.

A chemical analysis of a rock called Barnacle Bill - the first analysis of a rock on Mars - shows that it contains quartz, a silicon-rich mineral never before seen in significant amounts in rocks from anywhere but Earth.

The quartz, said geologist Hap McSween of the Mars Pathfinder team, shows that Mars, like Earth, must have had a dynamic geological history.

“I was floored when I saw that much silica,” said McSween, when the results of the Sojourner rover’s first chemical analysis of a rock were radioed back late Monday. “I was sure until I was handed those results that this was going to be basalt,” a much more common volcanic rock geologists already were sure was abundant on Mars.

Quartz is common in rocks on Earth, McSween said, and “Earth is a very unusual place - at least we thought so until last night.”

The Martian rock consists of about one-third quartz, the main ingredient in ordinary beach sand; one-third feldspar, the most common mineral in Earth’s crust; and one-third some other, not-yet-identified mineral such as pyroxene, the main component of the Martian meteorite in which possible signs of life were found last year.

The analysis also showed the rock to be very different from any of the 12 known meteorites on Earth that came from Mars, but it does contain chemical “fingerprints” that show its family resemblance to those Mars rocks.

“I think this rock contains the fingerprints of Mars all over it,” McSween said.

Rudolf Rieder, another geologist on the team, said the chemical analysis instrument, called the Alpha Proton X-ray Spectrometer, is working well on Mars: “We have actually not had such good data in the laboratory,” he said. That’s because the sensors work better at Mars’ cold temperatures - Tuesday’s high was about 5 degrees - than on Earth.

The analysis shows the rock may be a volcanic type called andesite, named for the Andes mountains in which it is commonly found. But it also might be a rock produced when several different types of minerals were fused together by a meteorite striking Mars, or - most interestingly - it could be a sedimentary rock. That would be more evidence that Mars once had large, long-lasting bodies of water that might have provided a habitat for the evolution of life.

But whichever type of rock it is, McSween said, it is virtually certain it contains abundant quartz - something that proves it went through “remelting followed by remelting followed by remelting.” To create quartz, you need a process called differentiation that causes different minerals to separate out from each other in the rock.

That means, he said, “you’ve got to have a heat source that lasts for a long time,” implying that Mars had “a more complex geological history” - more like Earth’s - than thought.

Meanwhile, the rover Sojourner has moved on to its next target, sidling up to a big rock nicknamed Yogi in preparation for analyzing its chemistry today.

The rover has also sent back its first analysis of the red soil of Mars, which turns out to be almost identical to that found by the two Viking landers on different parts of Mars in 1976 - mostly iron oxides, otherwise known as rust, which gives Mars its red color. The similarity suggests that this surface layer of dust, blown around frequently in planet-girdling dust storms, is spread quite uniformly over the planet.

“The more we look at the site, the more we are immensely happy,” said Golombek. “I could have only hoped this in my wildest dreams.”


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