NASA’s latest moon mission, LADEE, will spend three months studying the moon’s water cycle and atmosphere – two things most of us thought the moon didn’t have.
If all goes as planned, at 11:27 p.m. tonight, NASA will launch LADEE – the Lunar Atmosphere and Dust Environment Explorer, pronounced “laddy” – from its Wallops Island facility in Virginia. Most of the Eastern Seaboard will be able to watch the beginning of what sounds like an impossible mission: to study the moon’s atmosphere and water cycle.
Most of us learned in school that the moon doesn’t have either one of those. It turns out the story is a little more complicated, and a lot more interesting.
Past missions have looked down at the moon’s surface (Apollo, LCROSS) and interior (GRAIL), or even up to the lunar skies (Artemis), but LADEE is doing something different: “We’ll be looking sideways, through the atmosphere and dust, to understand what’s happening just above the surface,” says Sarah Noble, LADEE’s program scientist at NASA’s Washington, DC headquarters.
LADEE was created to answer “two mysteries,” says Rick Elphic, LADEE’s project scientist, “the first being the thin, tenuous, very exotic lunar atmosphere, utterly unlike our own; the second being this mysterious “lofted substance,” reportedly dust, that the Apollo astronauts saw above the surface.” …
The Lunar Atmosphere and Dust Environment Explorer (LADEE) was a NASA lunar exploration and technology demonstration mission. It was launched on a Minotaur V rocket from the Mid-Atlantic Regional Spaceport on September 7, 2013. During its seven-month mission, LADEE orbited around the Moon’s equator, using its instruments to study the lunar exosphere and dust in the Moon’s vicinity. Instruments included a dust detector, neutral mass spectrometer, and ultraviolet-visible spectrometer, as well as a technology demonstration consisting of a laser communications terminal. The mission ended on April 18, 2014, when the spacecraft’s controllers intentionally crashed LADEE into the far side of the Moon, which, later, was determined to be near the eastern rim of Sundman V crater. …
The Moon may have a tenuous atmosphere of moving particles constantly leaping up from and falling back to the Moon’s surface, giving rise to a “dust atmosphere” that looks static but is composed of dust particles in constant motion. According to models proposed starting from 1956, on the daylit side of the Moon, solar ultraviolet and X-ray radiation is energetic enough to knock electrons out of atoms and molecules in the lunar soil. Positive charges build up until the tiniest particles of lunar dust (measuring 1 micrometre and smaller) are repelled from the surface and lofted anywhere from metres to kilometres high, with the smallest particles reaching the highest altitudes. Eventually they fall back toward the surface where the process is repeated. On the night side, the dust is negatively charged by electrons in the solar wind. Indeed, the “fountain model” suggests that the night side would charge up to higher voltages than the day side, possibly launching dust particles to higher velocities and altitudes. This effect could be further enhanced during the portion of the Moon’s orbit where it passes through Earth’s magnetotail; see Magnetic field of the Moon for more detail. On the terminator there could be significant horizontal electric fields forming between the day and night areas, resulting in horizontal dust transport.
Also, the Moon has been shown to have a “sodium tail” too faint to be detected by the human eye. It is hundreds of thousands of miles long, and was discovered in 1998 as a result of Boston University scientists observing the Leonid meteor storm. The Moon is constantly releasing atomic sodium gas from its surface, and solar radiation pressure accelerates the sodium atoms in the anti-sunward direction, forming an elongated tail which points away from the Sun.