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. Last Updated: 07/27/2016

Color Was Key to Mars Rock Discovery

WASHINGTON -- Roberta Score knew the rock was extraordinary when she spotted it on an ice field among the Allan Hills of Antarctica. But she didn't consider that it could be a messenger of life from Mars.

"It was just lying on the surface," Score said Wednesday at a news conference. "I always thought that rock was special."

It has taken almost 12 years for science to show just how special that rock is. Known as Allan Hills 84001, the potato-sized specimen is the Mars meteorite that NASA researchers believe may contain evidence of ancient Martian life. Scientists around the world now are seeking pieces of the meteorite for study, hoping to prove or disprove the presence of life.

But the day that Score found the rock, Dec. 27, 1984, the most striking thing about it was its size and color.

Score, a geologist who works under contract with the Antarctic program of the National Science Foundation, was on her first expedition to the South Polar continent and was in a team of seven cruising on snow mobiles among the Allan Hills looking for meteorites.

At the time, Score said, she was awe-struck at the vast field of featureless, blue ice. "There was pure ice with no rocks around," she recalls. "Anything that you found in this particular ice field was a meteorite."

In one area, there were 15-foot-high pinnacles of ice, carved by the dry polar winds from ice that was thousands and thousands of years old. Just as they were leaving this area, her eye caught a spot of color. It was the rock, she said, "that is so famous now."

"It had a very green color to me," said Score. "I remember telling my colleague in Houston to just wait until he sees this green rock that is coming back."

Score followed the rock back to the Johnson Space Center where, in the same lab used to examine moon rocks, she unbagged Allan Hills 84001 in the cold light of the laboratory bench.

"When we pulled it out, it was just a dull gray rock," she said with a laugh. It had looked green because she was wearing tinted glasses and it was sitting on a blue ice, she said.

The National Science Foundation meteorite exploration program collects hundreds of meteorites each season from the Antarctica. Many, like Allan Hills 84001, have lain untouched in the ice for tens of thousands of years.

Ralph Harvey, a Case Western Reserve University geologist and leader of the annual search for meteorites, said that the Antarctic is an ideal place to look for rocks falling from space.

"If you wanted to find things that fall from the sky, you need to lay a great big white sheet and then watch it for a while," he said. Nature has provided the big white sheet with the polar ice field.

Meteorites have smashed into the ice field over eons and then slowly, at the rate of three to four inches a year, the ice is eroded by the dry winds. What is left behind are the rocks from the sky.

"We have a natural concentration mechanism," said Harvey.

The meteorites are generally sterile, since there are few bacteria in the ice fields. They are bagged immediately and the collectors "will not touch it with their hands," said Harvey.

More than 16,000 meteorites have been found in Antarctica, about half by the National Science Foundation teams, since scientists first started systematically search for space rocks in the ice fields.

Chemical readings collected by the Viking Mars landers established a chemical signature for Mars material. Using this, scientists have been able to identify 12 meteorites as having come from Mars, including a half-dozen that were found in Antarctica.

But even among the Mars specimens, Allan Hills 84001 is unusual. The rock has been dated to about 4.5 billion years old, making it among the oldest rocks known, said Harvey.