Passing comet peppered Mars with shooting stars, scientists say

(Reuters) - The comet that sailed by Mars last month spawned thousands of shooting stars per hour and created a new layer of ionized particles high in the planet's atmosphere, NASA scientists said on Friday.

At twilight, the Martian skies likely took on a yellowish hue from sodium in vaporized comet dust, creating a glow similar to sodium vapor lights commonly used in parking lots on Earth.

"To see (that) many shooting stars happening at once, I think it would have been really mind-blowing," planetary scientist Nick Schneider, with the University of Colorado in Boulder, told reporters on a conference call.

Scientists used a fleet of robotic spacecraft circling Mars to study Comet Siding Spring, which passed just 87,000 miles (139,500 km) by Mars on Oct. 19. That was less than half the distance between Earth and the moon, and 10 times closer than any known comet that has passed by Earth.

The comet was a rare visitor from the Oort Cloud, a spherically shaped reservoir beyond Neptune's orbit containing leftovers from the formation of the solar system some 4.6 billion years ago.

Comet Siding Spring "probably has never been in to the inner solar system before," said Jim Green, head of NASA's Planetary Science Division in Washington.

The comet also left an imprint on Mars, depositing thousands of pounds of dust into the atmosphere, far more than computer models had predicted.

NASA had moved its orbiting spacecraft so they would be behind Mars and shielded from dust impacts at the peak of the storm.

"I really believe that hiding them like that really saved them," Green said. "We ended up with a lot more dust than we ever anticipated."

Measurements taken before and after Siding Spring's approach show significant changes in Mars' upper atmosphere, including the addition of a new layer of charged particles and telltale chemical fingerprints of magnesium, iron and other metals shed by the passing comet.

Analysis is ongoing to determine the comet's size, composition and other attributes.

The comet is named for the Australian observatory that discovered it last year.

(Reporting by Irene Klotz; Editing by Leslie Adler)