[meteorite-list] Lunar Leonid Strikes

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 1 Dec 2006 18:10:25 -0600
Message-ID: <00c701c715a6$44859cb0$4e49e146_at_ATARIENGINE>

Hi, List,

> "Our best models of the lunar meteoroid
> environment predict a much lower rate -
> only 25% of what we are actually seeing."
> The problem may be with the computer models:
> "They're based on observations of meteors
> in the skies of Earth," and those data may not
> translate well to the Moon.

    Replace the phrase "those data may not
translate well to the Moon" with the phrase
"those data are flawed and worthless."

    The standard data is still the MORP figure
of 23,800 meteors (between 10 and 1000 grams)
per year. Back in 2000, I posted to the List a
new methodology for calculating the flux of rocks,
with four different ways of applying it, and all of
them produced an extimated spacerock flux of
3 to 4 times the MORP figure, or 80,000 to
100,000 rocks per annum.

    Giving credit: In the ensuing discussion, Rob
Matson also estimated a high flux (from ground
studies, I believe) and suggested that 100,000 to
120,000 was more likely.

    Getting my shave from Mr. Occam, the simplest
explanation of the observation of four times as many
meteoroids hitting the Moon as is predicted by bad
data from the Earth is that the data from Earth is
dead wrong and that there ARE four times as many
meteoroids (at least) than the bad data says.

    I say "at least" because there is no reason to think
these observations (nor any observations) have a 100%
perfect data recovery rate (MORP obviously did not),
so the "likely" rate is 4+ more than the 23,800 figure,
or north of 100,000.

    And please don't think I'm just bad-mouthing the
MORP project of long ago, a pioneering effort whose
results have stood because few carried on that kind of
search and research as they should have. The question
is why would their optically determined rate have been
so fractional of the reality?

    I'm just starting to think about that. More "dark"
(or slow) objects? More small objects? More objects from
less detectable directions? A different time distribution
than they assumed? Poorer detection limits?

> every 4 hours they observe the Moon,
> they see one bright flash caused
> by the impact of a large meteoroid...

    They don't say HOW large but at "normal" impact
speeds (Leonids are faster) that would have to be a
100 gram rock and probably bigger. The "four hour"
figure for the Moon would translate to a "big rock"
rate for the Earth of 40,000 "big rocks" per year.
(The range of sizes in the rate figure of 100,000+
is from 10 to 1000 gram.)

    Assuming a power law distribution for 10 to 1000
grams, the total would be: 100-1000 gram rocks = 40,000
and 10 to 100 gram rocks = 125,000, for a total flux of
165,000 spacerocks per year for the Earth. (If by "large"
they mean 60 gram and up, the rate would be about
125,000.)

    One more chunk of evidence to a picture that all
adds up to a greater "space rock" flux for Earth
than is generally believed.


Sterling K. Webb
-------------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Friday, December 01, 2006 1:10 PM
Subject: [meteorite-list] Lunar Leonid Strikes


>
> http://science.nasa.gov/headlines/y2006/01dec_lunarleonid.htm
>
> Lunar Leonid Strikes
> NASA Science News
> December 1, 2006
>
> Dec. 1, 2006: Meteoroids are smashing into the Moon a lot more often
> than anyone expected.
>
> That's the tentative conclusion of Bill Cooke, head of NASA's Meteoroid
> Environment Office, after his team observed two Leonids hitting the Moon
> on Nov. 17, 2006. "We've now seen 11 and possibly 12 lunar impacts since
> we started monitoring the Moon one year ago," says Cooke. "That's about
> four times more hits than our computer models predicted."
>
> If correct, this conclusion could influence planning for future moon
> missions. But first, the Leonids:
>
> Last month, Earth passed through a "minefield" of debris from Comet
> 55P/Tempel-Tuttle. This happens every year in mid-November and results
> in the annual Leonid meteor shower. From Nov. 17th to Nov. 19th both
> Earth and the Moon were peppered with meteoroids.
>
> Meteoroids that hit Earth disintegrate harmlessly (and beautifully) in
> the atmosphere. But the Moon has no atmosphere to protect it, so
> meteoroids don't stop in the sky. They hit the ground. The vast majority
> of these meteoroids are dust-sized, and their impacts are hardly felt.
> But bigger debris can gouge a crater in the lunar surface and explode in
> a flash of heat and light. Some flashes can be seen from Earth.
>
> During the passage through Tempel-Tuttle's debris field, Cooke's team
> trained their telescopes (two 14-inch reflectors located at the Marshall
> Space Flight Center) on the dark surface of the Moon. On Nov. 17th,
> after less than four hours of watching, they video-recorded two impacts:
> a 9th magnitude flash in Oceanus Procellarum (the Ocean of Storms) and a
> brighter 8th magnitude flash in the lunar highlands near crater Gauss.
>
> "The flashes we saw were caused by Leonid meteoroids 2 to 3 inches (5 to
> 8 cm) in diameter," says Cooke. "They hit with energies between 0.3 and
> 0.6 Giga-Joules." In plain language, that's 150 to 300 pounds of TNT.
>
> How do you get so much energy out of a 3-inch meteoroid? "Leonids travel
> fast - about 144,000 mph," he explains. "At that speed, even a 3-inch rock
> packs tremendous energy."
>
> For comparison, the ESA's SMART-1 probe crashed into the Moon on Sept.
> 2nd, delivering 0.6 Giga-Joules of energy to the lunar surface - the same
> as the brighter of the two Leonids.
>
> "Leonid impacts are as energetic as the crash of a 700-lb spacecraft!"
> says Cooke.
>
> With these latest detections, Cooke's group has tallied a dozen "lunar
> meteors" since Nov. 2005. Most were sporadic meteoroids--meaning they
> are part of no annual shower like the Leonids, but just random chips of
> asteroids and comets floating around in space. Cooke estimates that for
> every four hours they observe the Moon, they see one bright flash caused
> by the impact of a large meteoroid.
>
> And that's surprising. "Our best models of the lunar meteoroid
> environment predict a much lower rate - only 25% of what we are actually
> seeing." The problem may be with the computer models: "They're based on
> observations of meteors in the skies of Earth," and those data may not
> translate well to the Moon.
>
> The solution? "We need to spend more time watching the Moon," says
> Cooke. "With more data, we can draw stronger conclusions about the
> impact rate."
>
> NASA needs that kind of information to decide, e.g., if it's safe for
> astronauts to go moonwalking during a meteor shower; to calculate the
> necessary thickness of shielding for lunar spacecraft; and to answer the
> question, how often will a moonbase be punctured by a Leonid?
>
> Next up: The Geminid meteor shower on December 13th-14th. Once again
> Earth and Moon will be peppered with meteoroidsi - this time from the
> asteroid 3200 Phaethon. Says Cooke, "we'll be watching."
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
Received on Fri 01 Dec 2006 07:10:25 PM PST