Moon Crash Landing

[Christina]

August 30, 2006: Amateur astronomers, grab your telescopes. A spaceship is about to crash into the Moon, and you may be able to see the impact.The spacecraft: SMART-1, a lunar orbiter belonging to the European Space Agency (ESA).The impact site: Lacus Excellentiae (The Lake of Excellence), an ancient, 100-mile wide crater in the Moon's southern hemisphere.The time to watch: Saturday, September 2nd at 10:41 p.m. PDT (Sept. 3rd, 0541 UT).Why is SMART-1 crashing? There's nothing wrong with the spacecraft, which is wrapping up a successful 3-year mission to the Moon. SMART-1's main job was to test a European-built ion engine. It worked beautifully, propelling the craft in 2003 on a unique spiral path from Earth to the Moon. From lunar orbit, SMART-1 took thousands of high-resolution pictures and made mineral maps of the Moon's terrain. One of its most important discoveries was a "Peak of Eternal Light," a mountaintop near the Moon's north pole in constant, year-round sunlight. Peaks of Eternal Light are prime real estate for solar-powered Moon bases.But now SMART-1 is running low on fuel. It has to come down sometime—and soon—so ESA mission scientists decided to crash it in a place where the crash can be seen from Earth and studied. When SMART-1 hits the ground, it will explode in a flash of light. This won't be the sort of explosion we'd see on Earth. The Moon has no oxygen to support fire or combustion. Instead, the flash will be caused by rocks and soil made so hot by the impact that they suddenly glow. The area will be in complete darkness at the moment of impact, so much the better to see the flash. How bright will it be? No one knows. Estimates range from 7th to 15th magnitude. In other words, it might be bright enough for backyard telescopes--or so dim that even big professional observatories won't see a thing. The only way to find out is to look. "We'll be watching," says Bill Cooke, the head of NASA's Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Alabama. "Measuring the brightness of SMART-1's impact is important to our research."His group at the Marshall Space Flight Center has spent the last year watching things hit the Moon—not spacecraft, but meteoroids. "The Moon is under constant bombardment from meteoroids," says Cooke. "They hit the ground and explode just like SMART-1 will do." The Moon actually sparkles, slowly and faintly, as one space rock after another hits the ground.