Mars comet flyby has likely created "impressive meteor shower"

Comet Siding Spring may have created "an impressive meteor shower" that altered the upper atmosphere's chemistry of Mars for hours as it whizzed past the Red Planet last month, U.S. space agency NASA said Friday.

The comet made its closest approach to Mars on Oct. 19, at a distance of about 139,500 kilometers. This is about one-third of the distance between Earth and the moon and less than one-tenth the distance of any known comet flyby of Earth.

Data from observations carried out by two NASA and one European spacecraft showed that debris from the comet added "a temporary and very strong layer of ions" to the ionosphere, the electrically charged layer high above Mars.

"Dust from the comet impacted Mars and was vaporized high in the atmosphere, producing what was likely an impressive meteor shower," the space agency said in a statement. "This debris resulted in significant temporary changes to the planet's upper atmosphere and possible longer-term perturbations."

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, which recently arrived at Mars, observed intense ultraviolet emission from magnesium and iron ions high in the atmosphere in the aftermath of the meteor shower.

"Not even the most intense meteor storms on Earth have produced as strong a response as this one," NASA said. "The emission dominated Mars' ultraviolet spectrum for several hours after the encounter and then dissipated over the next two days."

The MAVEN spacecraft detected altogether eight different types of metal ions in the comet dust, including sodium, magnesium and iron.

Elsewhere above Mars, a joint U.S. and Italian instrument on European Space Agency's Mars Express observed a huge increase in the density of electrons in the ionosphere following the comet's close approach.

The increased ionization, like the effects observed by MAVEN, appears to be the result of fine particles from the comet burning up in the atmosphere, the space agency said.

Data from NASA's Mars Reconnaissance Orbiter (MRO) also showed the electron density of the ionosphere on the planet's night side, where the observations were made, was five to 10 times higher than usual.

Studies of the comet itself, made with MRO's high resolution imaging science experiment camera, revealed the nucleus is smaller than the expected 1.2 miles, or about two kilometers.

The MRO images also indicated a rotation period for the nucleus of eight hours, which is consistent with recent preliminary observations by NASA's Hubble Space Telescope.

Siding Spring is the first comet from the solar system's Oort Cloud to be studied up close. The Oort Cloud, well beyond the outer-most planets that surround the sun, is a spherical region of icy objects believed to be material left over from the formation of the solar system.