[meteorite-list] Lunar/Martian controversy

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:02 2004
Message-ID: <3FE5094C.D4C5FE9C_at_bhil.com>

Hi,

    Easiest expalnation is that the moonrocks we do find on Earth
have gotten here in a short timeframe. Probably zinged around
in the Earth-Moon system for a while and then had the bad luck
to smack us.
    And a "short" cosmic ray exposure age is a long time, at
least for us humans. Tektites have no CRE, proving that they
spent less than 25,000 years in space. In other words, there's a
lower bound to CRE ages, which corresponds to 0 years to 25,000
years. Of course, these tests may have become more refined and
and the lower bound smaller now.


Sterling K. Webb
----------------------------------------------------

j.divelbiss_at_att.net wrote:

> Sterling,
>
> First off I'm not about to challenge your mathematical grasp of this moon
> ejecta thing.
>
> I wondered how your facts about moon ejecta and its' avoidance of earth
> relates to Eric's comment about the short CRE age for lunar meteorites?
>
> The two comments don't jive to this simpleton.
>
> John
>
> > Hi,
> >
> > Just as it's hard to get to the Moon (from Earth, that is, I haven't made it
> > yet), it's even harder to get TO the Earth FROM the Moon.
> > Yeah, I know, it flies in the face of the obvious (Earth LOOKS flat)!
> > There's the
> > Moon just hanging around up there in the heavenly neighborhood, always right
> > next
> > door. Surely if you dropped a rock off of it, the rock would go plonk! straight
> > down
> > to my backyard, crushing the BBQ pit or splashing into the swimming pool!
> > Wouldn't
> > it? Did you hear a noise? Go look...
> > OK, you've thrown The Rock. You had to throw it as fast or faster than 2340
> > m/sec
> > or it would never escape the Moon. (Quite an arm you got there, kid!)
> > That means The Rock will reach the "neutral point" where the pull of the
> > Moon and
> > the tug of the Earth equal each other and cancel out. If you had really great
> > control
> > of that arm and managed to toss The Rock at exactly the right speed, it would
> > reach
> > the neutral point with ZERO velocity and it would STOP!
> > Yes, it would just hang out there, going nowhere and enjoying a fine view of
> > both
> > planetary bodies for the rest of Eternity (that's where I want to build my
> > retirement
> > home) or until the first little perturbation came along and then it would then
> > fall,
> > either back towards the Moon or on towards Earth.
> > Since the "neutral point" is very close to the Moon, the fall towards the
> > Earth
> > will convert all The Rock's potential energy of position into good old kinetic
> > energy. The Rock will achieve the full escape velocity of Earth in falling that
> > it
> > would take to get the heck off the planet if you were going the other way:
> > 11,200
> > m/sec.
> > Since in "real life" The Rock will probably have cruised past the "neutral
> > point"
> > with some residual velocity all its own, its terminal velocity will always BE
> > GREATER
> > THAN the Earth's escape velocity!
> > Hey wait! Slow down! You missed the turn! You drove right past it! It's back
> > there... That's life on the gravity freeway. So, unless The Rock is hideously
> > unlucky, it's going somewhere but that somewhere ain't the Earth!
> > Not only that, The Rock will have some vector given to it by the
> > circumstances of
> > its ejection and it WON'T be heading toward the one tiny spot of space where the
> > teensy-tiny Earth is going to be five days, two hours, 11 minutes and 43 seconds
> > later. (Kid, do you throw a curve ball?)
> > Since the big fat Earth only takes up 1/32,400 of the Moon's sky, the odds
> > of
> > hitting the Home Planet are small (I won't say "astronomically" small, I won't,
> > I
> > won't...)
> > And the "lucky" Rock, the one that heads straight and unerringly towards the
> > Earth dead center on target, right for your backyard? Well, since its entry
> > angle is
> > 90 degrees, straight screeeeeming vertically down through the atmosphere, it's
> > going
> > to burn up a long, long time before it reaches your BBQ pit or your swimming
> > pool.
> > So, almost all the Rocks thrown from the Moon will go their own way in the
> > solar
> > system, distaining a visit to the Big Brother planet, so close and yet so far
> > away.
> > Maybe, in 100,000 years, we and our planet might acidentally bump into some
> > Lunar
> > Escapees that have been wandering around in generally Earth-like solar orbits
> > and we
> > can get re-acquainted, but the odds are against it.
> > Bottom Line? The answer to "How do we get from the Moon to the Earth?" is
> > same as
> > the answer in the very old and not very funny joke about asking directions:
> > "You cain't get there from here."
> >
> >
> > Sterling K. Wdebb
> > ---------------------------------------------------------------
> >
> > j.divelbiss_at_att.net wrote:
> >
> > > Q: Do we think that it is possible for the moon's impact ejecta into space to
> > > escape Earth's gravity? I would think not, or very-very little.
> > >
> > > Cautious this time,
> > >
> > > John
> > >
> >
> >
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Received on Sat 20 Dec 2003 09:45:33 PM PST