Opportunity finds what it went to Mars looking for
Posted: February 1, 2004

With the pop of a champagne cork, a scientist announced Saturday that the Mars rover Opportunity has found scattered across the landing site a mineral that typically forms in water.

NASA's Mars exploration program is dedicated to finding evidence of past water on the Red Planet and eventually determining if life ever existed on Earth's cosmic neighbor.

In the days before driving off its lander, Opportunity used its infrared-sensing instrument, called the Miniature-Thermal Emission Spectrometer, or Mini-TES, to paint a picture of the landing site's mineral composition. The device is similar to one flown aboard the orbiting Mars Global Surveyor, which discovered the presence of hematite on the plains of Meridiani, prompting scientists to send the rover there for up-close examination.

"As you all know, we came to Meridiani in search of a particular mineral called hematite," Phil Christensen, spectrometer lead scientist, said at a news conference Saturday. "The hematite was discovered from an orbiting spectrometer looking down from Mars Global Surveyor. One of the first questions we wanted to answer when we got here on the surface was did we really find this hematite? And I'm here today to say that Mini-TES has indeed discovered hematite on the surface of Mars."

This spectrum captured by the Mars Exploration Rover Opportunity's Mini-Thermal Emission Spectrometer shows the presence of hematite in the soil at Meridiani Planum. Credit: NASA/JPL/Arizona State University
The proof is a squiggly line on a data graph. A laboratory spectrum of hematite, shown as the red curve, matches with the Mini-TES spectrum of the dark soil near the lander, shown as the yellow curve. Scientists say the W-shaped feature in the lines on the right indicates the hematite discovery.

Opportunity landed inside a crater 72 feet in diameter and 10 feet deep. The crater's gray soil granules have the hematite. But a portion of the crater's wall that has exposed bedrock, a white tabular outcrop, doesn't contain hematite.

"We have looked with Mini-TES at the white bedrock. One of our goals is to see what it is made of. All I can say at the moment is what it's not...That white unit does not have hematite in it," Christensen said.

Opportunity's arrival on Mars was shrouded by impact-cushioning airbags. After coming to rest inside the small crater, the bags deflated and the lander base opened its petals like a flower to reveal the rover packed inside. That wild ride of a landing disturbed the terrain, causing some areas of hematite on the dark Martian surface to seemingly disappear where the airbags hit the ground, exposing brighter red subsoil.

"Just next to the bounce marks we see a beautiful signature of hematite. In the bounce marks itself we do not see hematite. So this beautiful rover has already performed its first experiment before it even opened its petals. The airbags actually altered the surface enough so that it appears the hematite is carried in the coarse material and the fine red material underneath it we do not see this hematite signature.

"I think we are going to have a lot of fun exploring exactly where the hematite is," Christensen said.

The "footprints" left by Opportunity's landing airbags are creating curious questions in the hematite search. Credit: NASA/JPL
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Researchers are split in the debate of where the hematite went. Some think the gray granules were pushed beneath the surface's fine red material, others believe the hematite was pulverized.

But what does the disappearance tell scientists?

"I have lots of guesses. I'm sure they are all wrong. I'll share them anyway. That's the beauty of exploration that we are trying to find these answers," Christensen quipped.

"One of my worst fears was that the hematite was in the dust, this fine grain material, and it was everywhere and we would have a hard time tracking down the source. And without its source we would have a hard time tracking down its origin. It was extremely exciting and satisfying to see it in this coarse grain material as opposed to being in this fine grain sort of dust beneath that.

"I believe that the source of the material is in the rock unit that once lived on top of this white bedrock. And that is consistent with it being in this coarse grain material. Now, we can trace that material back to where it started and hopefully find its origin. Once we see it in place in its natural state, I think we'll have a much better clue of where it came from. Being in that coarse material is a huge first step at unraveling this mystery."

This high-resolution image captured by the Mars Exploration Rover Opportunity's panoramic camera highlights the puzzling rock outcropping that scientists are eagerly planning to investigate. Credit: NASA/JPL/Cornell
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How the hematite formed is another important question without an answer.

"The spectrum we see of hematite is distinctive between one of two origins -- a low temperature origin and a high temperature origin. From the data we have so far, it matches best to a low temperature origin," Christensen said.

On Earth, the mineral originates in various water, hydrothermal and volcanic situations.

Opportunity's science arm carries Mossbauer Spectrometer and Alpha Particle X-ray Spectrometer instruments to determine the composition of soil and rock samples. The arm will be placed on the hematite-bearing gray granules to determine what else is contained within.

Scientists hope to uncover other clues in the soil that will lend proof to a water origin theory or a volcanic one.

After completing its study of the soil and rock outcrop inside the landing crater, the robot geologist Opportunity will drive onto the smooth, flat plains of Meridiani.

"The view we see from orbit says this entire area is blanketed with hematite. It looked for the most part from orbit like it's not a wind blown material; it didn't come from a long way from somewhere else. The inference is there's a rock layer sitting on top of this white bed. As we get out of this crater that we're in, I think we will get up on a surface that is rich in hematite and we'll track it down."

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