http://science.nasa.gov/headlines/y2...ngmoondust.htm
Extracts:
At Cape Canaveral, not far from the launch pad where the space shuttle lifts off, there's a ragged hole in a chain link fence. Its message: Watch out for flying boulders.
"The powerful exhaust of the shuttle's solid rocket boosters blasts concrete out of the flame trench below the engines," explains physicist Phil Metzger.
This is no problem as long as people and equipment are kept at a safe distance, easily done. But, Metzger wonders, what if all this was happening on the Moon?
Here on Earth, no one pays much heed to dust or sand blasted out by a rocket launch because atmospheric drag rapidly slows the lightweight particles so they fall harmlessly to the ground a few meters from the blast. But on the Moon? There is no atmosphere to slow tiny particles. Small grit can travel enormous distances at high speeds, scouring everything in its path.
This isn't just theory. In November 1969, the Apollo 12 Lunar Module landed about 200 meters from Surveyor 3.
Metzger's team has analyzed dust-impact craters formed on Surveyor 3 and finds that the particles must have been traveling at least 400 to 1,000 meters per second. "In fact, they may have been traveling as fast as the exhaust gases of the lunar lander—that is, at 1 or 2 kilometers per second."
Particles speeding horizontally at 1.7 kilometers per second will travel literally halfway around the Moon. Boost that speed to 2 kilometers per second, and the projectiles can completely circle the Moon.
