[meteorite-list] A Meteoroid Hits the Moon

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jun 14 10:15:40 2006
Message-ID: <200606132344.QAA27948_at_zagami.jpl.nasa.gov>

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

A Meteoroid Hits the Moon
NASA Science News
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.

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 07:44:03 PM PDT