[meteorite-list] Lunar Flash Doesn't Pan Out

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:23:45 2004
Message-ID: <200303061713.JAA17262_at_zagami.jpl.nasa.gov>

http://skyandtelescope.com/news/current/article_890_1.asp

Lunar Flash Doesn't Pan Out
By J. Kelly Beatty
Sky & Telescope
March 5, 2003

For the past few weeks, impact aficionados have been abuzz over the
apparent confirmation that a house-size object struck the Moon on
November 15, 1953. The bright flare captured that evening by Leon H.
Stuart's backyard telescope matches the position of a small,
fresh-looking crater recorded by a spacecraft three decades later.
Bonnie J. Buratti (Jet Propulsion Laboratory) and Lane
Johnson, a student at Pomona College, unearthed this 1½-kilometer-wide
"smoking gun" in data from the Clementine orbiter, whose
high-definition cameras mapped the entire Moon in 1994.

Although the annals of amateur astronomy chronicle hundreds of such
transient lunar phenomena, almost all considered suspect by professionals,
Stuart's event stands apart because it was both seen and photographed.
That fact, together with the Clementine evidence, allowed Buratti and
Johnson to make a convincing case in January's issue of the scientific
journal Icarus. A press release even trumpeted "NASA Solves
Half-Century Old Moon Mystery."

But a little more historical digging would have shown that there was no
mystery to begin with. John E. Westfall (Association of Lunar and Planetary
Observers) has discovered that the bright blip seen by Clementine also
appears in a series of telescopic plates taken decades before Stuart
snapped his controversial exposure. In particular, Westfall notes, the
feature is "pretty obvious" in photographs made with Mount Wilson's
100-inch Hooker telescope in 1919. It also turned up on plates taken in
1937 with the 36-inch refractor at Lick Observatory and in others acquired
with Catalina Observatory's 61-inch reflector in 1966.

"It's kind of disappointing," Buratti said when told of Westfall's
revelation. "But it's more important to find that out." In researching
their paper, she and Johnson had examined a few telescopic images for a
small crater at the impact's presumed coordinates but found nothing. A
search of Lunar Orbiter frames, taken during the 1960s, also turned up
empty. They concluded that the candidate crater must be too small
(roughly 0.8 arcsecond across) to be resolved by ground-based efforts.

Even before Westfall came forward, doubts had been growing about the
Stuart-Clementine connection. For one thing, Stuart reported that the
bright flare lasted at least 8 seconds, an implausibly long fireball for
so small a crater. "We now know that an event of that scale should last
no longer than a second, but [Stuart] didn't," comments impact specialist
Alan W. Harris (Space Science Institute).

Other concerns were raised about the freshness of Buratti and Johnson's
candidate crater. Solar-wind bombardment causes lunar material to
darken and redden over time, but researchers believe such "space
weathering" takes place slowly over millions of years. Thus, if
20-meter-wide objects slam into the Moon frequently (often enough to make
Stuart's sighting statistically plausible), then the lunar landscape
should be peppered with 100,000 bright, fresh-looking splashes - and
it isn't. "You can't have it both ways," notes Harris.

Finally, the positional match wasn't as good as Buratti and Johnson first
thought. Careful measurement of Stuart's image by Sky & Telescope
editors Dennis di Cicco and Gary Seronik, as well as by Westfall, shows
that the flare is centered a full 1°, or 30 km, from the Clementine
candidate.

So, if it wasn't a flashy impact, what did Leon Stuart see and photograph a
half century ago? Some have suggested that it was a "point meteor," headed
directly at the camera, but that is ruled out by the flare's duration.
Moreover, the spot on the photographic plate is perfectly round, arguing
against a stray reflection or emulsion defect. In 1967 Stuart's original
underwent a battery of tests at the University of Arizona's Lunar
and Planetary Laboratory. But today the whereabouts of the original plate
are unknown, and without it the true mystery of "Stuart's event" may never
be solved.
Received on Thu 06 Mar 2003 12:13:49 PM PST