The moon's atmosphere is infinitesimal in comparison to the Earth's. But it turns out that our little buddy might have clouds -- of a sort, anyway.
According to a study published Wednesday in Nature, the moon has a permanent, lopsided, ever-changing dust cloud surrounding it. It's made of the dust on the moon's surface, which is stirred up by the bombardment of particles from space.
The new observations come from NASA's Lunar Atmosphere and Dust Environment Explorer, or LADEE, which launched in September 2013 and orbited the moon for about six months, catching over 140,000 of these impacts during that time with a detector designed and built by the University of Colorado Boulder.
You may have heard of clouds on the moon before -- on conspiracy Web sites. Several sources -- the Surveyor Probe, and the Apollo 17 mission -- have produced pictures of eerie, glowing cloud-like formations above our moon around sunrise and sunset. To some (especially on the Internet) that seems like a red flag for a faked space program. No atmosphere? No clouds! Ba humbug.
But even though the moon's atmosphere is indeed tiny, scientists now think they have evidence -- and a potential explanation -- for the phenomenon seen in those images.
According to the study team, there is indeed a dust cloud around the moon -- though it's much less dense than the one observed in the 1960s -- and it's caused by high-speed space collisions. The moon is covered in fine, sharp dust, and just a single particle of dust from a passing comet can hoist thousands of smaller dust particles up into the thin air. That's because space objects that eject particles at the moon are often speeding past our solar system's planets, moving in the opposite direction and creating high-speed (though physically tiny) collisions.
Every December during the Geminid meteor shower, the researchers report, the moon cloud gets a boost: The extra cascade of meteor dust particles kicks up extra moon dust, creating a thicker cloud for a few days. It's possible that there are other factors that determine the cloud's visibility, which could explain why it appeared so much more dense several decades ago.