Moon mission to look for 'hopping' water and 'electrified' dust
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 "laddie" – 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.Skip to next paragraph
In Pictures We love the moon
Subscribe Today to the Monitor
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.
RECOMMENDED: Are you a space whiz? Take our quiz!
Finding air on the airless moon
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."
As the astronauts flew over the moon, they saw what looked like "dust particles or aerosols," says Dr. Elphic, who is based at NASA Ames Research Center in Menlo Park, Calif. "But since the moon is an awfully good vacuum, and has only a thin trace of an atmosphere, we know that dust particles couldn't be suspended ... so it's a real mystery."
The moon is indeed airless, but it has an "exosphere" – that's the word for an atmosphere with so few particles in it that they drift around like ships at sea, never interacting with each other. Earth's exosphere is far, far out at the raggedy edge of our thick, gassy atmosphere, out past the International Space Station. On the moon, the exosphere is right at the surface, making it a "surface boundary exosphere." Surface boundary exospheres are actually more common than gaseous atmospheres, says Dr. Noble: Mercury has one, as do Pluto, most of the moons of the gas giant planets, and even some of the bigger asteroids. "It turns out to be the most common class of atmosphere" in our solar system, she says, "yet it is one we don't know much about."
LADEE's Ultraviolet and Visible Light Spectrometer (UVS) will scan sideways to analyze the exosphere and dust particles, while the Neutral Mass Spectrometer (NMS) and Lunar Dust Experiment (LDEX) will vacuum up whatever particles or dust the orbiter passes through. The UVS's telescope will pay special attention to the terminator, the line between day and night.
LADEE won't follow a circular orbit, because of the moon's "lumpy" gravitational field, but NASA scientists are taking advantage of that to time the closest approaches – when LADEE will skim just 12 miles above the moon's surface – to match up with passes by the terminator. "That's what our orbit is designed to optimize for: so we can go over the terminator as many times as we can, as close as we can, to see what's really going on," says Noble. LADEE will follow its uneven orbit for 100 Earth days, orbiting three times per day, so it will have a chance to observe the rising or setting sun some 600 times in its three-month mission.
As the terminator sweeps around the moon, bringing the rising sun across the lunar surface, scientists expect something very interesting to happen. Along with golden sunlight, sunbeams include photons strong enough to kick off the negatively-charged electrons, leaving the moon's sun-drenched side with a net positive electrical charge. The night side, the side of the moon facing away from the sun, has a net negative charge. At the terminator, breaking dawn brings with it an abrupt electrical change from negative to positive. The resulting current could zap dust grains into leaping sideways, some scientists have theorized.