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(meteorobs) Lunar impact

From Peiser Bennie's web site.

(1) MORE DOUBTS ABOUT LUNAR IMPACT IN 1953 

>From New Scientist, 8 January 2003 
http://www.newscientist.com/news/news.jsp?id=ns99993242

NEW CRATER REVIVES MOON MYSTERY
  
A mysterious flash on the Moon caught on camera 50 years ago is still
provoking disagreements about its origin. Astronomer Bonnie Buratti says her
new results show that the flash was caused by a 20-metre asteroid hitting
the Moon.

If Buratti is right, such impacts may be more frequent than thought - about
once every 30 years on the Earth, and every 500 years on the Moon. But other
asteroid watchers think the flash was due to a small meteor burning up in
Earth's atmosphere.

Amateur astronomer Leon Stuart's 1953 photograph of the Moon shows a light
spot near the centre of the Moon's visible surface. It would take a
half-megaton explosion to produce such a flash, says Buratti, of NASA's Jet
Propulsion Laboratory at Pasadena.

The resulting crater would not be visible from Earth, but it should appear
on close-ups taken by lunar probes. In a future issue of the journal Icarus,
Buratti reports a fresh impact scar at the site of the 1953 flash on images
collected by the Clementine spacecraft as it orbited the Moon in 1994. A
bright blanket of ejected material covers an area that is about 1.5
kilometres across, and the colour of the debris indicates that the crater is
relatively new.

Point meteors 
 
But the odds against such a big lunar impact are too long for Peter Brown of
the University of Western Ontario, who has used US military satellite data
to estimate meteor impact rates on the Earth. 

"I think they are going too far," he told New Scientist. Instead, he
believes that the flash was a meteor falling to Earth, which appeared as a
bright spot because it was moving directly towards the observer. 

Although such "point meteors" are rare, they are much more common than lunar
impacts. He is not impressed by the crater's appearance. "We have no
absolute criteria" for the age of lunar craters, he says. "'Fresh' could be
20 million years old."

Buratti calls Brown's claim "preposterous". She says Stuart was an
experienced observer, his half-second exposure shows no trace of motion, and
the flash was near a point on the leading edge of the Moon where impacts are
most likely. "Our identification of the crater validates Stuart's claim that
it was an impact." 
 
Jeff Hecht
 
Copyright 2003, New Scientist

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