[meteorite-list] Earth Rocks Could Have Taken Life to Titan (doubts)

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue Mar 21 22:17:35 2006
Message-ID: <004401c64d3a$09cf99c0$fae68c46_at_ATARIENGINE>

Hi, List, Mike

    You've put your finger on many of the problems
of getting a rock off a planet and launched into space.
When it was first determined that Martian meteorites
WERE Martian, there were choruses of "no way!"
No impact model anticipates such ejection; none, even
today, shows unequivocally how it could happen.

    And Mars, of course, is "easy." Its gravity and escape
velocity is much less than the Earth's and its atmosphere
is much thinner. Still, the models do not predict it. In fact,
they say still it's impossible. The problem is it happens.
We got the rocks. They arrived here on Earth. So it
MUST be possible.

    Naively, it seems that getting rocks knocked off the
Moon to the Earth should be easy. It turns out it's easy
to get them knocked off the Moon, but hard (for reasons
of flight dynamics) to get them to the Earth. Mercury
would seem to be a good source (no air, weak gravity)
and Gladman's earlier simulations say we should have
them here, but we don't seem to have any indisputable
Mercurian meteorites.

    Venus has gravity almost as great as the Earth's and
a much thicker atmosphere. Gladman's earlier simulations
say there should be lots of Venusian meteorites getting to
Earth, but again the museum cases are notoriously short
of Venusian achondrites!

    The difficulty of getting a rock out of the Earth's
atmosphere from an impact is much harder than you
present it. When a stone enters the atmosphere at
high velocity, it encounters the thinnest air first, allowing
a gradual loss of velocity. But a stone leaving from the
bottom of the atmosphere encounters the densest air
at the first moment when it has the highest velocity.
The chief problem is rapid ablation.

    This has been studied extensively in the problem
of how tektites are produced and high velocity ejecta
get vaporized in rapid ablation long before they get
out of the atmosphere. The bigger and faster the rock,
the worse the problem, and rocks will get burned away
before they travel very far.

    Yet, we know it can happen; Mars proves that.
Naturally, I have a theory... When an impactor enters
the atmosphere, it creates a tunnel of rarefied air in
its path by pushing the air out of the way. The heating
of the atmosphere in that path helps to keep it from
collapsing instantly. This is all true for even a small
object, your ordinary meteor. The long rolling thunder
after the explosion of a meteor that succeeds in getting
down to the lowest levels of the atmosphere is the sound
of air closing that rarefaction tunnel.

    When a large object which will become an impactor
passes through the atmosphere, the rarefaction tunnel
becomes much larger, with lower internal pressures,
and persists much longer and extends for greater distances.
It may effectively reach "out" of the atmosphere. Any piece
of the target surface given a high enough velocity in the right
direction could escape through the rarefaction tunnel
without meeting enough resistance to destroy it. Aiding
in the process is a plasma plume from the impact that
"blows back" along the flight line, rarefying it even more
and extending the duration of the "tunnel." However,
not very many impact-shocked rocks head in that
direction!

    My theory is that a sufficiently large impactor (100's
of meters) creates a much more efficient and powerful
rarefaction tunnel than we usually imagine. First, there
is a vast quantity of very high temp plasma created on
the forward face of the re-entering object. I omit a long
winded explanation of why it is that the plasma organizes
as a series of toroidal rings surrounding the "tunnel,"
but it does. When a current circles the surface of a
torus transversely, it generates a circulating central
current that keeps the torus from collapsing to smaller
diameters and, if strong enough, may even expand it.
As long as the currents flow, the "tunnel" remains open.

    You end up with a "vacuum pipe" extending from the
surface of the Earth to the top of the atmosphere. A vast
quantity of target materials, not from the point of direct
impact but from further out, are thrown into the air at
low velocities and with little shock. The "vacuum pipe" is
disconnected from the object (it no longer exists). The
impact plasma plume has flashed up through the "pipe"
and it now remains open in the lower atmosphere to
suck up the surface atmosphere which contains lots
of low velocity debris.

    This "plug" of air, thoroughly filled with these relatively
unshocked debris, is sucked up the pipe. The passage
of atmosphere through the "pipe" cools the plasma to
the point where the ions re-combine, the charges vanish,
the plasma mechanism fails, and the "pipe" begins to
collapse from the bottom up. The vacuum above the
debris-filled air sucks it upward as the "pipe" collapses,
accelerating the mass to escape velocity, and ejecting
the debris into space.

    Thus, we have a natural replication of the conditions
of the mechanism of a successful launch: low impact,
gradual acceleration, little or no ablative friction. The
many studies of Martian meteorites show low or minimal
levels of shock and heating, and so forth, nothing to
indicate a violent mechanism of ejection, so there must
be a more effective and less stressful mechanism than
raw blasting power.

    Anyone else want to design a "conveyor"?


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

----- Original Message -----
From: "Mike Fowler" <mqfowler_at_mac.com>
To: <meteorite-list_at_meteoritecentral.com>
Cc: "Mike Fowler" <mqfowler_at_mac.com>
Sent: Monday, March 20, 2006 11:18 AM
Subject: [meteorite-list] Earth Rocks Could Have Taken Life to Titan
(doubts)


>> He says only boulders at least 3 metres across could punch out through
>> the Earth's atmosphere and escape the planet's gravity, and that only
>> extremely powerful impacts could achieve this. The cause of such impacts
>> would be comets or asteroids between 10 and 50 kilometres wide, Gladman
>> told New Scientist: "The kind of thing that killed the dinosaurs."
>
> I have my doubts. (again) Someone please correct me if I err in my
> numbers or logic.
>
> A rock being ejected into space is somewhat like a meteorite falling to
> Earth, but in reverse.
> To be ejected into space the rock must leave Earth's atmosphere with
> escape velocity. That means, it must have been accelerated to a velocity
> GREATER than escape velocity to account for the velocity lost punching
> thru Earths atmosphere.
>
> Question #1 Can an impact accelerate rocks greater than 3 meters in
> diameter to 15 kilometers per second,or more, without shock melting
> them, or pulverizing them?
>
> Meteorites entering the Earth's atmosphere push ahead of them a column of
> air until the pressure on the meteorite exceeds the crushing strength of
> the meteorite, at which point it explodes and the surviving pieces fall
> under the influence of gravity.
>
> Question #2 If a whole rock, 3 meters or more in diameter, could be
> accelerated to 15 kps intact, wouldn't the back pressure of the
> atmosphere exceed the strength of the rock resulting in fragmentation
> into pieces, just as happens to virtually all stony meteorites passing
> thru the Earth's atmosphere with similar velocity? Such pieces will not
> coast into space, on the contrary they will be retarded by the remaining
> atmosphere, and quickly loose escape velocity.
>
> I would never say something is impossible.
>
> But I have my doubts about hundreds of millions of Earth Boulders being
> ejected thru the atmosphere unless you can overcome the above 2
> objections.
>
> Any comments Sterling or others?
>
> Mike Fowler
> Chicago
>
>
>
>
>
>
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Received on Tue 21 Mar 2006 05:51:48 PM PST