Mars’ Barnacle Bill Is Like Earth Rocks, Rover Finds
Presenting the first chemical analysis ever of a rock on Mars, the rover Sojourner has discovered that our neighboring planet is much more Earthlike than scientists previously thought.
The rough-surfaced rock named Barnacle Bill, which Sojourner studied during its second day on Mars, reveals clear evidence of repeated melting and reheating, suggesting that it has been cooked and cooked again within the Martian crust. This implies that the Red Planet remained hotter longer than researchers suspected.
“More things are going on in the Martian crust than we thought,” said project scientist Matthew Golombek, who added that scientists couldn’t yet explain their findings.
“This is a real surprise,” said Hap McSween, a geologist from the University of Tennessee who is working on the Pathfinder project. “We were not expecting to see rock of this composition.”
Barnacle Bill, to the researchers’ surprise, appears to contain a good deal of quartz--a common mineral on Earth. Previously, they thought Mars would be almost entirely basalt--the most common type of volcanic rock on Earth. Quartz rises to the top when basalt is cooked repeatedly, like cream rising to the top of unhomogenized milk.
The ability to compare the chemical ingredients of Martian rocks with terrestrial rocks will vastly expand geologists’ understanding of the processes that gave birth to the planets, including Earth.
“It’s not just the Earth anymore. . . . It’s a historic moment,” Golombek said.
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By spitting subatomic particles at rocks and measuring the radiation that comes back, Sojourner’s alpha X-ray proton spectrometer can see almost every element. The instrument cannot actually see the quartz directly. Instead, it sees elements, which in turn fit together in various ways to form minerals, like quartz.
Barnacle Bill is loaded with the element silicon, and “so much silicon demands that it has quartz,” McSween said.
None of the meteorites from Mars that geologists have studied--including the famous rock found on Earth that appeared to contain evidence of ancient fossil life--had substantial quantities of quartz.
It makes sense to find quartz on Earth because the motion of continental plates continually plows rocks deep under the surface and recycles them in different forms. However, Mars has no plate tectonics. So researchers still do not understand what could be reheating the rocks to form quartz.
In some ways, Barnacle Bill is similar to rocks found in the South American Andes. It is probably volcanic in origin, McSween said, because “it looks like Swiss cheese,” and the gases from volcanic eruptions blow bubbles in rocks. However, a similar Swiss cheese pattern could be produced by other processes--including meteor impacts and mixing with water.
In other ways, however, Barnacle Bill is like other Mars meteorites, McSween said, and “has the fingerprints of Mars all over it.”
Researchers continued to be delighted with the overall variety of rocks at the Pathfinder landing site. “This site is really a rock festival,” McSween said.
Camera scientist Peter Smith showed off the first parts of a panoramic picture of the site, called the Monster Pan, which was supposed to be available Tuesday, but was put off until today.
He did point out some intriguing new features on the Martian surface, including a rock with a crack in it and several newly named rocks, Shark and Wedge. “I’m having trouble remembering all the rock stars,” he said.
A white semicircle in front of the bear-shaped rock called Yogi looked like the remains of an ancient puddle of standing water, the kind of place where ancient Martian pond scum might have found a home.
The landscape revealed a diverse collection of rocks and soils. “I don’t have a clue how to explain this,” Smith said. “It’s quite beautiful.”
In chemical composition, the soil analyzed by Sojourner is very similar to that seen by Viking landers of 21 years ago. Although the Viking landers could test soil, they did not have rovers and could not visit rocks and determine their ingredients.
Researchers were somewhat worried that the omnipresent Martian dust might seep into Sojourner’s spectrometer and contaminate the results. “We could get dust in our eyes,” said instrument scientist Rudolph Reider of the Max Planck Institute in Germany. That is a problem because the instrument only reads the top layer of what it sees, and its analysis is therefore only skin deep.
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Today, Sojourner will take close-up stereo pictures of Yogi in preparation for doing a chemical analysis, probably Thursday. It will also look at rocks named Casper and Scoobie Doo.
Meanwhile, the rover has been continuing to study the tracks it makes with its wheels to learn about the Martian soil. On Monday, Sojourner made “the first wheelie on Mars,” Golombek said.
The Hubble Space Telescope will also start looking at Mars today. When Hubble looked at Mars a week before the Pathfinder landing, it saw white clouds. Pathfinder, however, found itself on a very dusty planet.
By comparing the Hubble view and the Pathfinder view at the same time, researchers will be able to determine whether the Mars weather has changed since Hubble took its first images, or whether dust on Mars just looks like white clouds from far off in space.
Nicholas Thomas, also of the Planck Institute, showed images of Mars’ tiny moon Deimos taken from “the first astronomical observatory on Mars.” The small camera aboard Pathfinder isn’t very good for doing astronomy, he said, but it should help researchers measure the dust in Mars’ atmosphere. That dust gave rise to a “spectacular” blue sunset.
Although looking at the tiny blue ball of Earth from Mars isn’t of great scientific importance, Thomas said, “we’ll do it anyway,” for emotional reasons.
The weather report on Mars was the same as it has been from the outset of the mission, with a high of 5 degrees Fahrenheit and light winds. “Weather on Mars at this season is pretty boring,” Thomas said.
But if the engineers can keep the Pathfinder going for 50 or 60 days, “we will see dramatic changes” as Mars moves into fall.
