[meteorite-list] Lunar velocities...
From: meteorites_at_space.com <meteorites_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:43 2004
On Tue, 27 March 2001, "Robert Beauford" wrote:
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> <DIV><FONT size=2>"These "stretch" tektites are a clear indication of
> terrestrial origin as how could such a form survive if they had been formed on
> the moon and then entered the Earth's atmosphere at 7+ miles
> <DIV><FONT size=2></FONT> </DIV>
> <DIV><FONT size=2>Steve's comment above got me curious. It seems like
> ejecta from the moon need not reach a cosmic velocity or earth orbital velocity,
> just an escape velocity or orbital velocity of the moon. It seems, more
> specifically, that any fragment with a speed over the escape velocity of the
> moon, and a vector that points it inside the orbit of the moon around
> the earth (slightly less than 50% of all lunar ejecta?), and insufficient
> residual speed to send it back out of that orbit, would fall to earth.
> This should alow for some very slow objects reaching earth (and thus less
> ablation loss and entry alteration) What is this necessary and maximum
> speed? Please note, I am not advocating a lunar origin for tektites, just
> idly, and perhaps ignorantly, wondering if lunar meteorites might enter the
> atmosphere slower than some other meteorites.</FONT></DIV>
> <DIV><FONT size=2>-Robert Beauford : )<BR><BR></DIV></FONT></BODY></HTML>
What you say is correct. If tektites came from the moon then their entry velocities would be no slower than 7 miles per/sec, which is also the escape velocity for objects leaving the earth. I would imagine that most of them, if ejected at speeds significantly greater than the escape velocity of the moon would also be ejected out of the earth's gravity well to then establish their own orbits around the sun.
(If so, this I imagine would create a problem with the tektite strewnfields as they are on the earth. How could there be the distributions that are observed is this were the case)
If say, a rock was ejected off of the moon with just enough velocity to leave its gravity well, and also to be thrown into the earth's gravity well, but with not enough residual speed to leave it at the moon's distance-- then it would fall to the earth gaining speed all the way. It, like the Apollo moon modules would strike the earth's atmosphere at 36,000 feet per/sec, about 7 miles per/sec, which is significantly slower than most meteoroids.
This may also be the case for lunites.
That the tektites have strewnfields that reveal singular events, is telling. If they were ejected out into space with sufficient speed to leave the earth's gravity well then they would have orbits that would allow for them falling at more random times. In other words, they would be falling all the time. (Not very frequently, but enough over the past 800,000 years and longer, to smudge the strewnfields so as to make them less defined. (you just don't find any Georgia tektites in Southeast Asia, or vica versa).
So, I think the implications of this pretty much rules out lunar origin, for if an (volcanic or impact) were so violent as to have ejected such a huge amount of glass off of the moon and onto earth it would also have thrown an equal if not greater amount out into the depths of space to establish orbits of glassy debris in independent paths around the Sun.
In any case, whether tektites enter the earth's atmosphere from a Solar orbit, or directly from the moon, ablation will occur, and for spherical objects or dumbells that orient the result would be a flange of glass around the object.
(In the 1950's it was proved that flanged buttons were the product of hypersonic velocities through the earth's atmosphere when balls of glass were inserted into the exhaust of rocket engines to simulate hypersonic speeds of 5 miles per/sec. Result-- perfectly formed flanged buttons)
But this does not mean that because there are such flanged buttons that they came from the moon. They very well may have been created on earth in some strange impact event, thrown up to a height of several thousand miles, cooled then fell back to earth.
(From a altitude of 2000 or more miles the re-entry speed would be sufficient enough to create a flange.)
Mystery of mysteries-- Maybe in our lifetimes everyone will come to a consensus as to how these strange objects formed.
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Received on Tue 27 Mar 2001 03:02:43 PM PST