for National Geographic News
A mysterious area of layered bedrock on Mars that has puzzled scientists was formed by a volcanic explosion, new research shows.
Spirit, one of NASA's two Mars rovers, mapped the tabletop-like formation, which scientists call Home Plate because of its shape resembling the home plate in baseball.
Analysis of the data collected by Spirit shows that the outcrop was probably formed by layers of ejected volcanic materials.
The larger grains of debris were buried under finer materials and later rearranged by wind, NASA scientists believe.
"It's the first really powerful evidence that either rover has found for explosive materials [on Mars]," said Steve Squyres, an astronomer at Cornell University and principal investigator of the rovers' mission.
His team's findings are reported in tomorrow's issue of the journal Science.
Located in Mars's Gusev crater, Home Plate stands a few yards high and 260 to 295 feet (80 to 90 meters) across.
(See a map of Mars.)
Scientists had advanced several theories to explain how it formed, including the effects of wind and sand deposits.
But when Spirit began exploring the structure last fall, scientists noticed that Home Plate contained a "bomb sag," a depressed area on the ground where a rock, or "bomb," would have fallen.
"That provided compelling evidence that this was a case where there had been an explosion," Squyres said.
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