WASHINGTON -- They came from Mars, not in peace, but in pieces. Scientists are confirming that 15 pounds of rock collected recently in Morocco fell to Earth from Mars during a meteorite shower in July.

This is only the fifth time in history that scientists have chemically confirmed Martian meteorites that people witnessed falling. The fireball was spotted in the sky six months ago, but the rocks weren't found on the ground in North Africa until the end of December.

This is a unique opportunity for scientists trying to learn about Mars' potential for life. So far, no NASA or Russian spacecraft has returned bits of Mars, so the only samples scientists can examine are those that fall in a meteorite shower.

Scientists and collectors are ecstatic, and the rocks are fetching big bucks because they are among the rarest things on Earth. The biggest rock weighs more than 2 pounds.

"It's nice to have Mars sending samples to Earth, particularly when our pockets are too empty to go get them ourselves," said former NASA sciences chief Alan Stern, director of the Florida Space Institute at the University of Central Florida.

A special committee Tuesday of meteorite experts, including some NASA scientists, confirmed test results that showed the rocks came from Mars, based on their age and chemical signature.

Astronomers think that millions of years ago, something big smashed into Mars and sent rocks hurtling through the solar system. After a long journey through space, one of those rocks plunged through Earth's atmosphere, breaking into smaller pieces.

Most other Martian meteorite samples sat on Earth for millions of years before they were found, which makes them tainted with Earth materials and life. These new rocks, while probably contaminated because they have been on Earth for months, are purer. The last time a Martian meteorite was found fresh was in 1962. All the known Martian rocks on Earth add up to fewer than 240 pounds.