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Moon dust is filling in the astronaut footprints

Traci Watson
Special to USA TODAY
Neil Armstrong portrait of Buzz Aldrin with the photographer and the Lunar Module reflected in his gold-plated visor, Apollo 11, July 1969

Scientists have discovered a lopsided cloud of moon dust hovering over that shining orb in the night sky.

Each speck of dust hangs above the moon for only a few minutes before showering back onto the lunar surface. But the nimbus of dust constantly replenishes, forming a permanent feature around the moon.

The pattern of dust falling back to its home "in due time … will fill in craters," says the University of Colorado, Boulder's Mihaly Horanyi, who led the team that found the dust cloud. "Eventually this will erase the footprints of the astronauts."

Buzz Aldrin's boot print on the lunar surface, Apollo 11, July 1969

The moon wears this hazy veil thanks to the comet dust that speckles the solar system. When a bit of dust from a comet's tail slams into the moon, the collision kicks up thousands of particles of moon dust, which are carried high above their resting place on the lunar surface, Horanyi says. The moon-dust cloud was especially thick during the Geminid meteor shower, when the Earth and its sidekick swing through a particularly thick belt of debris.

Thick is relative. From near the moon's surface to more than 70 miles up, the cloud tops out at only 260 pounds of dust. But the rise and fall of all those dust grains helps form the moon's character, Horanyi says. The team's findings stem from data collected by NASA's LADEE spaceship, which reached the moon in 2013. The study appears in this week's Nature.

Though LADEE managed to find microscopic specks of dust, it did not find the answer to a lunar mystery dating back nearly 50 years. To researchers' confusion, many Apollo astronauts orbiting the moon reported a strange glow on the lunar horizon. One of the Apollo 17 astronauts even took pen to paper to sketch what he labeled "definite linear streamers" of light out his spacecraft's window.

The strange sightings have been attributed to light bouncing off dust above the moon, but the phenomenon has remained – and likely will remain -- controversial. Though LADEE found dust, it did not find the dense dust cloud needed to account for the Apollo observations.

"There's dust and there's dust," says Johns Hopkins University's Paul Feldman. "I'm willing to say we still don't understand what (the Apollo astronauts) saw."

LADEE certainly "revealed a dust cloud," says Anthony Colaprete of the NASA Ames Research Center, but "the story's not completely done being told." However, LADEE has given scientists a useful tip: it's possible to study airless, dusty worlds by examining their dust halos. "It's like sampling a surface without having to put (down) a lander … which is obviously a lot easier," Colaprete says.

Scientific scrutiny of the moon's dust will continue, but without LADEE's help. In 2014, the spacecraft, running low on fuel, was deliberately steered into the lunar surface at high speed. Now, after a frenzied career of dust research, LADEE has found eternal rest in a handful of dust.

Photos: Fascinating new scientific discoveries:

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