[meteorite-list] A Meteoroid Hits the Moon

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed Jun 14 10:17:43 2006
Message-ID: <mouu82hut9sevda7q5nu9rjk6fnkp6i9h7_at_4ax.com>

http://science.nasa.gov/headlines/y2006/13jun_lunarsporadic.htm

June 13, 2006: There's a new crater on the Moon. It's about 14 meters wide, 3
meters deep and precisely one month, eleven days old.

NASA astronomers watched it form: "On May 2, 2006, a meteoroid hit the Moon's
Sea of Clouds (Mare Nubium) with 17 billion joules of kinetic energy?that's
about the same as 4 tons of TNT," says Bill Cooke, the head of NASA's Meteoroid
Environment Office in Huntsville, AL. "The impact created a bright fireball
which we video-recorded using a 10-inch telescope."

Lunar impacts have been seen before--"stuff hits the Moon all the time," notes
Cooke--but this is the best-ever recording of an explosion in progress:

The video plays in 7x slow motion; otherwise the explosion would be nearly
invisible to the human eye. "The duration of the fireball was only four-tenths
of a second," says Cooke. "A student member of our team, Nick Hollon of
Villanova University, spotted the flash."

Taking into account the duration of the flash and its brightness (7th
magnitude), Cooke was able to estimate the energy of impact, the dimensions of
the crater, and the size and speed of the meteoroid. "It was a space rock about
10 inches (25 cm) wide traveling 85,000 mph (38 km/s)," he says.

If a rock like that hit Earth, it would never reach the ground. "Earth's
atmosphere protects us," Cooke explains. "A 10-inch meteoroid would disintegrate
in mid-air, making a spectacular fireball in the sky but no crater." The Moon is
different. Having no atmosphere, it is totally exposed to meteoroids. Even small
ones can cause spectacular explosions, spraying debris far and wide.

According to the Vision for Space Exploration, NASA is sending astronauts back
to the Moon. Are these meteoroids going to cause a problem?

"That's what we're trying to find out," says Cooke. "No one knows exactly how
many meteoroids hit the Moon every day. By monitoring the flashes, we can learn
how often and how hard the Moon gets hit."

The work is underway. Using a computerized telescope built by Rob Suggs and
Wesley Swift of the Marshall Space Flight Center, Cooke's group is monitoring
the night side of the Moon "as often as ten times a month, whenever the lunar
phase is between 15% and 50%."

During a telescope test last November 7th, Suggs and Swift recorded an explosion
on their very first night of observing. A piece of debris from Comet Encke
struck the plains of Mare Imbrium, making a crater about 3 meters wide.

Right: The light curve of the May 2nd explosion in Mare Nubium. [Larger image]

Now that regular monitoring has begun, Cooke's group has already found a second
impact, the May 2nd event, in only 20 hours of watching. This time, they
believe, the impactor was a random meteoroid, "a sporadic," from no particular
comet or asteroid.

"We've made a good beginning," says Cooke, but much work remains. He would like
to observe all year long, watching the Moon as it passes in and out of known
meteoroid streams. "This would establish a good statistical basis for planning
[activities on the Moon]."

Is it safe to go moon walking during a meteor shower? How much shielding does a
lunar habitat need? Does the Moon have its own meteor showers, unknown on Earth?

Expect the answers in a flash.
Received on Tue 13 Jun 2006 10:58:51 PM PDT