Eric, List, all,
Asteroids are traveling at super high velocity when they impact...
The most common collision in a group of objects with similar
orbits is with two objects with similar orbits. Oh, yes, in the
movies it's always something that comes racing out of far
nowhere and -- Smack! But in the real world, it's more like
jostling each other.
I mean, the biggest threat to Earth would be something in
an orbit similar to our own, right? We want our orbit to
ourselves!. So it is for asteroids. What is the most likely
speed of that kind of collision? It's the same speed that
it would take to go from asteroid to asteroid.
Now, in SciFi stories, folks are always hopping from one
asteroid to another in dinky little jumper spaceships, but
in fact most transfer orbits between asteroids require a
delta-vee of 4000 m/sec to 5000 m/sec. If you calculate
Hohmann orbits between Ceres and Vesta, Pallas and Vesta,
Pallas and Ceres, they all fall in that range.
That means it's twice as hard as taking off from the Moon
(or landing on the Moon) or about half the effort of getting to
low Earth orbit. If one asteroid wanders into the path of
another or intersects its orbit when it's there, the impact
velocities between them could be as low as a few thousand
meters per second or as high as six to eight thousand
meters per second, depending on the specifics of the
encounter.
On the other hand, here at the bottom of a deep gravity
well, even a standstill object is going to pick up 11,200
meters per second falling in, plus any encounter velocity
it might have started with. In other words, we get whacked
but good with an average encounter speed of 20,000+
meters per second
So oddly enough, most asteroidal collisions are gentler
than collisions with the Earth. They're more than enough
to do real damage of course, including disrupting whole
bodies, but that's because asteroids are weaker (except
for solid irons).
As for the speed of fragments "blown off" by a collision,
they depart at speeds less than the collision speed that
spawned them. Statistically, at about collision speed times
the square root of two, for an average.
There is a small chance for more energetic collisions. That's
when one object has an odd orbit: high eccentricity orbits
and high angle collisions, retrograde versus prograde, all
sorts of odd things, but the point is that we call'em "odd"
because they're infrequent when compared to ALL collisions.
Fragments generated at the very inner edge of the asteroid
zone can get here in 50,000 to 80,000 years, stuff from the
main belt in a few to ten million years, stuff from the outer
asteroid zone (type D and P) much longer. But time is even
longer than space is big...
So they tell me.
Sterling K. Webb
--------------------------------------------------------------------------------
----- Original Message -----
From: "Meteorites USA" <[email protected]>
To: <[email protected]>
Sent: Monday, July 12, 2010 5:02 PM
Subject: [meteorite-list] How Long from Asteroid to Meteorite?
Hi Greg S., Richard, List,
Greg's question about the furthest known celestial body from which we
have a meteorite is very interesting! And it brings up another very
interesting question related to distance...
If we're not sure of the furthest asteroid or comet we've got
meteorites from, can we at least figure out how long it takes
meteorites to get here from the asteroid belt once asteroids collide?
We know meteorites come from a variety of planetary and asteroid
bodies, and even some are suspected cometary debris. But...
I've always wondered how long it would take a piece of asteroid debris
to impact our planet after an asteroid collision.
Asteroids are traveling at super high velocity when they impact,
creating massive explosive power comparable to multiple nuclear
explosions at once. Wouldn't that launch debris in ALL directions at
cosmic velocity? If this ejecta debris is moving at 15,000 to 25,000
MPH how long would it take to reach our planet from the asteroid belt?
Would it slow considerably between there and here given the
gravitational forces exerted by Mars, Jupiter, the Moon, or even our
planet? Would most of the debris get caught by other planets, or even
in stable orbits around the Sun? How do you figure orbits of this
smaller debris which come from these collisions when you can't even
see it?
I know, sorry for all the questions... but I want to know darnit! ;)
Regards,
Eric
On 7/12/2010 2:25 PM, Richard Kowalski wrote:
Hi Greg.
You probably will not be able to get a definitive answer to this one.
Meteorite parent bodies are from asteroids and the most likely
mechanism to inject asteroids and their fragments into orbits that
intersect the earth is perturbations by Jupiter. This places most
asteroidal meteorites parent bodies in the outer Main Belt.
As far as I know, there are no meteorites that have all the expected
properties that a cometary meteorite should have, so that makes the
Main Belt the most distant source of meteorites currently known.
If a cometary meteorite is discovered, it's parent ultimately would
be the Oort Cloud, so that would change "The most distant" record
holder instantly.
Campins and Swindle presented a summary on what properties a cometary
meteorite should have at the 39th Lunar and Planetary Science
Conference in 2008. It can be read here:
http://www.lpi.usra.edu/meetings/LPSC98/pdf/1004.pdf
--
Richard Kowalski
Full Moon Photography
IMCA #1081
--- On Mon, 7/12/10, Thunder Stone<[email protected]> wrote:
From: Thunder Stone<[email protected]>
Subject: [meteorite-list] What Meteorite is 'From' the farthest
location from the Earth?
To: [email protected]
Date: Monday, July 12, 2010, 1:17 PM
Hi List:
I was wondering if it is know what meteorite(s) is from (or
was created) at the farthest point from Earth? I know they
come from the asteroid belt and perhaps from comets, but
wouldn't it be really neat to have a meteorite that was
formed or (from) the farthest distance from Earth in your
hand: I think it would.
Greg S.
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