NASA's next moon mission will send the Lunar Atmospheric and Dust Environment Explorer (LADEE) to study what causes the moon's mysterious glow.
NASA's new LADEE orbiter could be described as a space-age vacuum cleaner, designed to suck up the fine lunar debris that shrouds the moon at high altitudes.
But this is no cosmic clean-up job. Instead, the space agency's latest lunar mission — set to launch Sept. 6 — is really about making sense of the moon's mysterious characteristics.
Not much is known about the composition of the ultra-thin atmosphere surrounding Earth's closest celestial neighbor. For example, what causes the "dust fountains" that streak the sky during lunar sunsets and sunrises? And could high-altitude debris lofting as high as 62 miles off the moon's surface be due to electrostatic levitation?
"There are good reasons to be interested in the dust on the moon's surface," Brian Day, a NASA spokesperson with the Lunar Science Institute, said, calling the moon "an ideal place to do astronomical observations."
But if that charged dust is indeed drifting around the surface of the moon, it could complicate those observations because moon dust is angular, sharp, sticky and quite an irritant.
"You don't want to be exposed to it and you definitely don't want to breathe it," Day said. "It could get into the joints of your space suit; it could attach itself to all kinds of instrumentation."
So that's why NASA is launching the LADEE orbiter (short for Lunar Atmospheric and Dust Environment Explorer), a 6 ½-foot-long spacecraft weighing more than 700 pounds, complete with a hatch that will draw in dust samples for further study.
"Dust flies in and will hit a curved plate in the back of the instrument, causing ionization and creating an electrical signal that we'll be able to study," Day said.
WHY THE SURFACE OF THE MOON CATCHES SUNLIGHT
The dust could explain some of the ethereal optics first observed in the 1960s by the Surveyor moon missions. At the time, scientists had believed the lunar sky was empty, but robotic landers' cameras caught something surprising when the sun was just below the moon's horizon.
"They would capture these fascinating glows in the sky of the moon," Day said. "If the lunar sky was empty, you wouldn't see a glow like that. There would be nothing to reflect the light to the camera. There was something above the surface of the moon that was catching the sunlight."
Astronauts later saw this phenomenon of possible "dust fountains" first-hand. Eugene Cernan famously sketched the light displays during the Apollo 17 missions, gazing out the window of the command module as the sun was just below the horizon.
Unlike Earth, the moon is not protected by a strong magnetic field, nor does it have a thick atmosphere. This creates a "charged space weather environment" in which nighttime and daytime sides of the moon react very differently with dust due to the presence of light photons "slamming" into the surface and knocking electrons off atoms.
"That means the surface dust can get positively charged," Day said. "Imagine dust particles sitting on the surface of the moon, getting this positive charge as they start to repel each other, and lifting up."
As for why the moon is so dusty in the first place, look at its cratered surface. That's the result of billions of years of bombardment from comets and meteorites spreading bits of pulverized rock about the lunar surface.
LADEE's journey to the moon is expected to take about a month. The spacecraft will then spend about 100 days orbiting before it returns to Earth.
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