According to a team of scientists led by Prof Mihaly Horanyi of the University of Colorado Boulder, the Moon is engulfed in a permanent but asymmetric dust cloud that increases in density during the annual meteor showers.
Moon. Image credit: Gregory H. Revera / CC BY-SA 3.0.
The lunar cloud was discovered using data from NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE). It’s made up primarily of small dust grains kicked up from the Moon’s surface by the impact of high-speed, interplanetary dust particles.
“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,” explained Prof Horanyi, who is the first author of the paper published in the journal Nature.
The first hints of the lunar cloud came in the late 1960s when NASA cameras aboard unmanned landers captured a bright glow during lunar sunsets.
Several years later, Apollo 15 and 17 astronauts reported a significant glow above the Moon’s surface when approaching sunrise, a phenomenon which was brighter than what the Sun alone should have been able to generate at that location.
“Since the new findings don’t square with the Apollo reports of a thicker, higher dust cloud, conditions back then may have been somewhat different,” Prof Horanyi said.
The scientists also found that the density of the lunar cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles.
“Many of the cometary dust particles impacting the lunar surface are traveling at thousands of miles per hour in a retrograde, or counterclockwise 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,” Prof Horanyi explained.
“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.”
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M. Horányi et al. 2015. A permanent, asymmetric dust cloud around the Moon. Nature 522, 324–326; doi: 10.1038/nature14479
