[meteorite-list] NASA Astronomers Spot Rare Lunar Meteor Strike

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat Dec 24 18:31:49 2005
Message-ID: <200512242330.jBONUEM21883_at_zagami.jpl.nasa.gov>

http://www.nasa.gov/centers/marshall/news/news/releases/2005/05-190.html

NASA Astronomers Spot Rare Lunar Meteor Strike

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256.544.0034)

News Release: 05-190
December 23, 2005

Astronomers at NASA's Marshall Space Flight Center, Huntsville, Ala.,
have recorded a small but powerful meteoroid strike in the night on the
moon's surface.

On Nov. 7, using a 10-inch-diameter telescope, astronomers recorded a
tiny blip northwest of Mare Imbrium, the moon's "Sea of Showers." Such
impacts are not uncommon, but it was only in 1999 that scientists first
recorded a lunar strike as it happened.

"People just do not look at the moon anymore," said Dr. Robert Suggs,
Space Environment team lead in the Natural Environments Branch of the
Marshall Center's Engineering Directorate. "We tend to think of it as a
known quantity. But there is knowledge still to be gained here."

As NASA plans to return to the moon, the agency has a need to understand
what happens after lunar impacts in order to protect lunar explorers. On
Earth, the atmosphere vaporizes most small meteoroids, leaving nothing
behind but a brief streak of light. The vacuum environment on the moon,
however, means there is nothing to slow incoming meteoroids before they
strike.

"The likelihood of being struck by a meteoroid on the lunar surface is
very, very small," said Bill Cooke, an astronomer in Marshall's
Meteoroid Environment Office. "The challenge is learning what happens to
high-velocity ejecta, the debris kicked up by a meteoroid strike, which
is not hindered by atmospheric friction or Earth gravity. What threat
does that debris pose to humans or equipment?"

Suggs, who heads the impact study, used commercial software tools to
study the video frame by frame, and spotted a very bright flash. The
burst of light diminished gradually over the course of five video
frames, each 1/30th of a second in duration. Suggs called in Cooke, and
both scientists agreed that the bright light was an impact flash,
captured by video from some 248,000 miles away.

Immediately, the team began ruling out other possible causes. Two
telling characteristics won out - the gradual diminishment of the flash
rather than an on-off "winking" effect, and its motionlessness. A
flicker of light from a moving satellite, Cooke noted, would have
appeared to shift perceptibly, even in five brief frames of video.

Suggs and Cooke next consulted star charts and lunar imaging software
and determined the meteoroid was likely a Taurid, part of an annual
meteor shower active at the time of the strike. Based on the amount of
light produced the object was roughly five inches in diameter, traveling
more than 60,000 mph, and may have gouged a crater nearly 10 feet in
diameter out of the moon's surface.

The Taurids, which approach Earth from the direction of the Taurus
constellation, are believed to be ancient remnants of comet Encke, which
orbits the Sun every 3.3 years.

NASA scientists previously studied lunar meteor strikes during the
Apollo moon program, but lacked the sophisticated video cameras and
high-powered image processors to capture the tiny, telling flashes. Now,
however, as NASA readies its next-generation spaceship to carry
explorers back to the moon for potential long-term stays, Suggs and
Cooke say lunar impact research is more vital than ever.

"Large-scale lunar facilities are sure to be well-protected, using
impact-resistant technologies much like those developed to shield the
space shuttle and the International Space Station," Suggs said. "We want
to support additional measures that safeguard personnel working in the
lunar field - early-alert systems, emergency protective measures and new
technologies that will mitigate risks from flying impact debris."

For more information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home

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http://science.nasa.gov/headlines/y2005/22dec_lunartaurid.htm

An Explosion on the Moon
NASA Science News
December 23, 2005

December 23, 2005: NASA scientists have observed an explosion on the
moon. The blast, equal in energy to about 70 kg of TNT, occurred near
the edge of Mare Imbrium (the Sea of Rains) on Nov. 7, 2005, when a
12-centimeter-wide meteoroid slammed into the ground traveling 27 km/s.

What a surprise," says Marshall Space Flight Center (MSFC) researcher Rob
Suggs, who recorded the impact's flash. He and colleague Wes Swift were
testing a new telescope and video camera they assembled to monitor the
moon for meteor strikes. On their first night out, "we caught one," says
Suggs.

The object that hit the moon was "probably a Taurid," says MSFC meteor
expert Bill Cooke. In other words, it was part of the same meteor shower
that peppered Earth with fireballs in late October and early November
2005. (See "Fireball Sightings
<http://science.nasa.gov/headlines/y2005/03nov_taurids.htm>" from
Science_at_NASA.)

The moon was peppered, too, but unlike Earth, the moon has no atmosphere
to intercept meteoroids and turn them into harmless streaks of light. On
the moon, meteoroids hit the ground--and explode.

"The flash we saw," says Suggs, "was about as bright as a 7th magnitude
star." That's two and a half times dimmer than the faintest star a
person can see with their unaided eye, but it was an easy catch for the
group's 10-inch telescope.

Cooke estimates that the impact gouged a crater in the moon's surface
"about 3 meters wide and 0.4 meters deep." As moon craters go, that's
small. "Even the Hubble Space Telescope couldn't see it," notes Cooke.
The moon is 384,400 km away. At that distance, the smallest things
Hubble can distinguish are about 60 meters wide.

This isn't the first time meteoroids have been seen hitting the moon.
During the Leonid meteor storms of 1999 and 2001, amateur and
professional astronomers witnessed at least half-a-dozen flashes ranging
in brightness from 7th to 3rd magnitude. Many of the explosions were
photographed simultaneously by widely separated observers.

Since the Leonids of 2001, astronomers have not spent much time hunting
for lunar meteors. "It's gone out of fashion," says Suggs. But with NASA
planning to return to the moon by 2018, he says, it's time to start
watching again.

There are many questions that need answering: "How often do big
meteoroids strike the moon? Does this happen only during meteor showers
like the Leonids and Taurids? Or can we expect strikes throughout the
year from 'sporadic meteors?'" asks Suggs. Explorers on the moon are
going to want to know.

"The chance of an astronaut being directly hit by a big meteoroid is
miniscule," says Cooke. Although, he allows, the odds are not well known
"because we haven't done enough observing to gather the data we need to
calculate the odds." Furthermore, while the danger of a direct hit is
almost nil for an individual astronaut, it might add up to something
appreciable for an entire lunar outpost.

Of greater concern, believes
Suggs, is the spray - "the secondary meteoroids produced by the blast." No
one knows how far the spray reaches and exactly what form it takes.

Also, ground-shaking impacts could kick up moondust, possibly over a
wide area. Moondust is electrostatically charged and notoriously clingy.
(See "Mesmerized by Moondust
<http://science.nasa.gov/headlines/y2005/21nov_abbas.htm>" from
Science_at_NASA.) Even a small amount of moondust can be a great nuisance:
it gets into spacesuit joints and seals, clings to faceplates, and even
makes the air smell when it is tramped indoors by moonwalkers. Could
meteoroid impacts be a source of lunar "dust storms?" Another question
for the future....

Suggs and his team plan to make more observations. "We're contemplating
a long-term monitoring program active not only during major meteor
showers, but also at times in between. We need to develop software to
find these flashes automatically," he continues. "Staring at 4 hours of
tape to find a split-second flash can get boring; this is a job for a
computer."

With improvements, their system might catch lots of lunar meteors. Says
Suggs, "I'm ready for more surprises."
Received on Sat 24 Dec 2005 06:30:14 PM PST