New York, June 18 (IANS): The Moon is engulfed in a permanent but lopsided dust cloud made of tiny dust grains kicked up from the Moon's surface by the impact of high-speed, interplanetary dust particles, says a study.

"A single dust particle from a comet striking the Moon's surface lofts thousands of smaller dust specks into the airless environment and the lunar cloud is maintained by regular impacts from such particles," said lead researcher Mihaly Horanyi, professor at University of Colorado Boulder.

Knowledge of the dusty environment in space has practical applications, Horanyi noted in the study published in the journal Nature.

Knowing where the dust is and where it is headed in the solar system, for example, could help mitigate hazards for future human exploration, including dust particles damaging spacecraft or harming astronauts.

Many of the cometary dust particles impacting the lunar surface are travelling at thousands of miles per hour in counter-clockwise orbit around the Sun -- the opposite orbital direction of the solar system's planets.

This causes high-speed, near head-on collisions with the dust particles and the Moon's leading surface as the Earth-Moon system travel together around the Sun, Horanyi said.

The cloud was discovered using data from NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which was launched in September 2013 and orbited the Moon for about six months.

"Identifying this permanent dust cloud engulfing the Moon was a nice gift from this mission."

The researchers found that the cloud increases in density when annual events like the Geminids spew shooting stars.

The Geminid meteor showers occur each December when Earth plows through a cloud of debris from an oddball object called Phaethon, which some astronomers describe as a cross between an asteroid and a comet.

"When these 'beams' we see from meteors at night hit the Moon at the right time and place, we see the cloud density above the Moon skyrocket for a few days," Horanyi said.