[meteorite-list] Exploding Lunar Eclipse

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 27 Aug 2007 16:50:17 -0700 (PDT)
Message-ID: <200708272350.QAA01051_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2007/27aug_explodingeclipse.htm

Exploding Lunar Eclipse
NASA Science News
August 27, 2007

August 27, 2007: Most people appreciate lunar eclipses for their silent
midnight beauty. NASA astronomer Bill Cooke is different: he loves the
explosions.

On Tuesday morning, Aug. 28th, Earth's shadow will settle across the
Moon for a 90-minute total eclipse: full story
<http://science.nasa.gov/headlines/y2007/03aug_dreamyeclipse.htm>. In
the midst of the lunar darkness, Cooke hopes to record some flashes of
light--explosions caused by meteoroids crashing into the Moon and
blasting themselves to smithereens.

"The eclipse is a great time to look," says Cooke, who heads up NASA's
Meteoroid Environment Office (MEO) at the Marshall Space Flight Center.
The entire face of the Moon will be in shadow for more than two hours,
offering more than 7 million sq. miles of dark terrain as target for
incoming meteoroids.

Lunar explosions are nothing new. Cooke's team has been monitoring the
Moon since late 2005 and they've recorded 62 impacts so far. "Meteoroids
that hit Earth disintegrate in the atmosphere, producing a harmless
streak of light. But the Moon has no atmosphere, so 'lunar meteors'
plunge into the ground," he says. Typical strikes release as much energy
as 100 kg of TNT, gouging craters several meters wide and producing
bursts of light bright enough to be seen 240,000 miles away on Earth
through ordinary backyard telescopes.

"About half of the impacts we see come from regular meteor showers like
the Perseids and Leonids," says MEO team-member Danielle Moser. "The
other half are 'sporadic' meteors associated with no particular asteroid
or comet."

The MEO observatory is located on the grounds of the Marshall Space
Flight Center in Huntsville, Alabama, and consists of two 14-inch
telescopes equipped with sensitive low-light video cameras. Moser and
colleague Victoria Coffey will be on duty Tuesday morning.

During the eclipse, they hope to catch an elusive variety of meteor
called Helions.

"Helion meteoroids come from the direction of the sun," Cooke says, "and
that makes them very difficult to observe." They streak across the sky
most often around local noon when the sun's glare is too intense for
meteor watching.

Wait a minute. Meteors from the sun? "The sun itself is not the source,"
he explains. "We believe Helion meteoroids come from ancient sungrazing
comets that laid down trails of dusty debris in the vicinity of the sun."

No one can be certain, however, because Helion meteoroids are so devilishly
difficult to study. Astronomers see them only in small numbers briefly
before dawn or after sunset. Attempts to study Helions via radar during
the day have been foiled, to a degree, by terrestrial radio interference
and natural radio bursts from the sun - both of which can drown out
meteoroid "pings."

Enter the eclipse.

During the eclipse, the Man in the Moon (the face we see from Earth)
will be turned squarely toward the sun???"perfect geometry for
intercepting Helion meteoroids," says Moser. "And with Earth's shadow
providing some darkness, we should be able to see any explosions quite
clearly."

"Watching Helion meteoroids hit the Moon and studying the flashes will
tell us more about their size, velocity and penetration," she adds.
That, in turn, will further the MEO's goal of estimating meteoroid
hazards to spacecraft and future Moon-walking astronauts.

No one has ever seen a lunar impact during an eclipse, "but there's a
first time for everything," Cooke says. Stay tuned to Science at NASA for
results.
Received on Mon 27 Aug 2007 07:50:17 PM PDT