Hi, Bob, Chris, List
The three factors that get a meteorite intact to the surface of
the Earth are : a) slow entry velocity, b) low angle of incidence,
and c) an aerodynamically useful shape to start with.
The third factor is moot on the Moon. The first two still
apply. So, some chunk, once in a thousand times, hits low and
slow, slow being 5000 to 7000 mph!
Of course, the "slowing" that atmosphere applies is the major
cause of the destruction of meteoroids trying to reach the Earth,
by heat and a max dynamic pressure which often exceeds the
strength of the stone. None of that applies on the Moon, either.
Slow or fast, the item will strike the lunar surface unretarded.
If the incoming is small and fast, it will vaporize, or at very
moderate velocities, be smashed to a fine powder, or some
combination of the two.
If the incoming is large, the story is different. Think of the
stone as having a "front" pole and a "rear" pole. The "front" pole
of the stone will vaporize explosively. The shock wave will
fragment the "rear" pole and spall fragments away. The velocity
of the shock wave is generally the same as the velocity of impact,
but it starts inside the stone, hence gets to the "rear" pole just
in time to spall the last patch of surface off (more if slow;
less if fast; nothing if really fast).
Bob mentioned Canyon Diablo's. All the Canyon Diablo's
that ever were are the result of "rear spall."
So lunar (meaning on the Moon) meteorites would be a small
number of scattered fragments. They would be scattered over a
vast landscape (or is that lunascape?) that is itself littered with
innumerable lunar crust fragments produced by aeons of
bombardment, all pounded to pieces (or to powder).
Meteorite hunting on the Moon would be at least as difficult
as meteorite hunting on the Earth, like finding a pebble in a
rockpile, with neither shape (no aerodynamic friction to sculpt
it), nor color (space weathering will alter the colors of the stone)
to make any one stone stand out from millions of others.
No, make that harder than meteorite hunting on the Earth.
Just as on Mars (or anywhere), the likeliest survivor
would be a good sized iron (Hoba, Cape York, Wilmette).
If it didn't melt on impact or fragment to tiny pieces, someday,
someone might notice it... It'll be on the front page of all the
newspapers: the Tycho Times, Luna City Ledger, the
Copernicus Chronicle...
Sterling K. Webb
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----- Original Message -----
From: "Chris Peterson" <[EMAIL PROTECTED]>
To: <Meteorite-list@meteoritecentral.com>
Sent: Thursday, August 31, 2006 11:06 PM
Subject: Re: [meteorite-list] Meteorites on the moon
"Unaltered by atmospheric pressure" also implies unslowed by any
atmosphere. So everything that hits the Moon is doing so at a minimum of
around 2.5 km/s, and usually a lot more. I don't think you'll find many
meteorites.
As thin as the Martian atmosphere is, it is enough to provide
aerobraking. The rover cameras have apparently recorded a few meteors.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "Bob Evans" <[EMAIL PROTECTED]>
To: <Meteorite-list@meteoritecentral.com>
Sent: Thursday, August 31, 2006 9:54 PM
Subject: [meteorite-list] Meteorites on the moon
Can you imagine hunting meteorites on the moon?
Crustless Diogenites, Eucrites, Howardites strewnabout everywhere.
Pristine Pallasites unaltered by atmospheric pressure or humidity
sticking out of the lunar dust like a gem.
How excited Nasa was when they found one on Mars. I'm surprised there
wasn't a manless mission planned to go to the moon to extract and
return some of these pristine meteorites utilizing a rover. Obviously
it would be tremendously expensive, but, compared to what is spent on
the mars mission as well as expeditions in the arctic its a no -
brainer.
The moon is a meteorite goldmine. 100% impact rates, craters
everywhere pinpointing the spot of impact.
I wonder if Nasa found one gram out of the relatively miniscule amount
of specimens returned from the moon to be of non-lunar origin.
I believe if we want to make monumental advancements in Meteoritics we
need to take advantage of the abundance on the moon. Who knows what
never before seen meteorite types are laying up there right now.
What do you think, Mike? You don't have to worry about any Norwegian
export laws.
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