March 23, 2014
Lunar orbiter LADEE has picked up traces of dusty lunar atmosphere with its LDEX instrument. The observation will help us better understand other airless celestial bodies suspected to have some sort of similar atmosphere.
LADEE in lunar orbit, artist's impression. Credit: NASA
Since the late 1960s and early 1970s, scientists have been trying to figure out if the Moon has an atmosphere. Certainly, there's no air on the Moon, but by trying to detect sunlight reflecting off dust molecules high above Moon surface, they were looking for traces of an atmosphere made of dust.
NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) has a different approach. Launched in September 2013, it's been in lunar orbit since early October. Flying between 13 and 60 kilometres above the surface, it has been collecting dust particles with its Lunar Dust Experiment (LDEX) instrument. Since it's picking up one to two dust particles every minute, it appears that the Moon has an atmosphere after all.
"We do have an atmosphere. It's made out of the dust particles," said Mihaly Horanyi, who is the lead scientist for LADEE’s LDEX. "Apparently that happens very often, roughly once or twice per minute."
This seems to puzzle geologist Harrison Schmitt, the last astronaut that walked on the Moon in 1972, who said, "Once in a while you'll see some regolith that's been thrown up on a rock, but not a covering of fine dust. I can't in my own mind figure out a way in which you could have levitation of dust that is so precise up and down that it doesn't get on the rocks."
Logic suggests that if there was a dusty atmosphere, all of lunar surface would be covered with dust equally, so if there is an atmosphere on the Moon, further explanations are needed.
LADEE also detected bursts of dust approximately every 10 days, when its LDEX instrument picks up up to 300 particles per minute. This is believed to be caused by microasteroids bombarding lunar surface and ejecting dust upwards.
"It's as if you were flying through the nearby cloud of ejecta from an impact that took place right next to you," said LADEE project scientist Richard Elphic.
LADEE will crash into the Moon's surface on April 21 this year. These last 30 or so days, it will spend at about 4.5 kilometres above the surface, providing more details. The study should help in understanding airless celestial bodies that could have atmosphere made of dust, such as Mercury or other moons in the solar system.
Before it crashes, however, LADEE will have to stay in the "air" during the lunar eclipse that will happen on April 15. "LADEE wasn't designed to survive this very long eclipse, but we expect it to and if we do we'll do science measurements on down until we crash into the surface of the Moon," added Elphic.