How the Sun, and scientists, suspend Moon dust in the sky
Even on a clear day, the view from Earth doesn’t include the blackness of space reaching down to the horizon. At night you get something closer to this view, but we usually end up looking at a sky filled with light scattered off various bits of dust and air instead. Without an atmosphere full of molecules to scatter sunlight, you can assume the view from an asteroid, or the Moon, is much more stark. With nothing but a tiny layer of particles barely comparable to an atmosphere, it follows that Apollo astronauts were fairly baffled by the huge, dusty corona they encountered when orbiting the Moon.
The glow that was seen by both Apollo astronauts and robotic explorers orbiting the Moon was not exactly an approximation of the blue glow you can see around Earth. Dubbed the Lunar Horizon Glow (LHG), sunlight was being scattered in a narrower crescent close to where the Moon was experiencing sunrise or sunset. The fact that collection of dust could scatter sunlight to create the appearance of a glow wasn’t so strange. The question was, with no atmosphere, wind or other obvious means to carry this dust up to 62 miles above the Moon’s surface, how as any of it getting off the ground?
Positive and negative particles
A leading hypothesis about what’s launching the dust is basically a lunar version of static electricity. During the Moon’s day, the sunlight hits some dust, knocking off electrons and ionizing the molecules, giving them an electrostatic charge. At night, plasma blowing from the Sun would do the same process to dust in the dark, only instead of giving it a positive charge, it would end up with a negative charge. Both versions would mean a lot of charged dust repelling neighboring particles with the same charge, which in some cases may be enough knock some dirt high into the Moon’s sky.
This mechanic was recently demonstrated in a laboratory on Earth. Micon-sized dust particles were exposed to ultraviolet radiation or plasmas to see how much they could be charged up for a jump into space. They could be charged enough to move away from each other, and its estimated that they would have been able to leap around four inches into the air if Earth had the lesser gravity present on the Moon.
Understanding exactly how these plumes work is important to future exploration efforts, because electrically charged particulate could easily interact with visiting spacecraft, with less than glowing results if we’re not prepared.
Source: Mysterious Moon Light Made by Glowing Dust Fountains by Zoe Macintosh, Space.com
