[meteorite-list] Witnessed fall lunars?

From: Melanie Matthews <miss_meteorite_at_meteoritecentral.com>
Date: Tue, 7 Sep 2010 22:18:28 -0700 (PDT)
Message-ID: <29733.71617.qm_at_web114014.mail.gq1.yahoo.com>

<"Mars is farther away and not protected by a companion and its closer to the
asteroid belt so it receives many more impacts than the moon."

Not "many more." Only a factor of two greater for Mars, but the average
velocity of the impactors is only 60% as great.>

To add, the side of the Moon that always faces away from Earth would be just as
vulnerable to bombardment as Mars is..


 -----------
-Melanie
IMCA: 2975
eBay: metmel2775
Known on SkyRock Cafe as SpaceCollector09

I eat, sleep and breath meteorites 24/7.



----- Original Message ----
From: Randy Korotev <korotev at wustl.edu>
To: meteorite-list at meteoritecentral.com
Sent: Tue, September 7, 2010 2:06:15 PM
Subject: Re: [meteorite-list] Witnessed fall lunars?


> MikeG asks:

> "Is there a theory for why there have been no witnessed falls of lunar
> meteorites? It seems odd to me that we have 4 Martian witnessed falls
> (Shergotty, Chassigny, Zagami, Nakhla, and almost Lafayette) and no
> lunars."

One issue is that these 5 meteorites are 5 kg, 4 kg, 18 kg, 10 kg, and 0.8 kg in
mass. Only 3 lunars are >4 kg in mass.

Another issue (probably more important) is that lunar escape velocity is only
2.4 km/s and very little material ejected from the Moon is going much faster
than that. This velocity compares with 20-40 km/s for asteroidal meteorites.
Is a rock entering the atmosphere at 2.4 km/s going to noticeably incandesce? I
don't know. I believe that the space shuttle hits the atmosphere at ~7.7 km/s.

Melanie asks:

"I asked this a while ago on Greg Catterton's forum, and I was told that rocks
from the moon aren't as solid (tough) as Mars rocks, and therefore are less
likely to survive entry... yet what about all these Howardites?"

Although breccias, most of the lunar meteorites are very tough rocks. Any rock
that survives being blasted off the Moon isn't going to disintegrate in Earth's
atmosphere any more than an asteroidal or martian meteorite.

Steve says:
"The moon is close to the earth and material knocked off the moon has a
relatively short time to reach the earth."

Compared to what? Some lunar meteorites took a million years or more to reach
Earth.

"Mars is farther away and not protected by a companion and its closer to the
asteroid belt so it receives many more impacts than the moon."

Not "many more." Only a factor of two greater for Mars, but the average
velocity of the impactors is only 60% as great.



Randy Korotev
Washington University in St. Louis

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Received on Wed 08 Sep 2010 01:18:28 AM PDT