[meteorite-list] Earth Ejecta Could Have Seeded Life on Europa

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 26 Aug 2011 22:36:17 -0500
Message-ID: <1172DEC4779140318F9894587FDB9F83_at_ATARIENGINE2>

Hi, Al, Bernd, List,

> Takes less energy to fall in than out.

Actually, the reverse is true. It much harder
for a meteorite from a oplanetary surface to
fall in than to fall out. It's counter-intuitive,
but true.

Imagine you've just escaped the Earth's gravity
and you'd like to visit Mars. The minimum
energy cotangential orbit that touches the
Earth's orbit at aphelion is 32.7 km/s and at
perihelion at Mars is only 21.5 km/s, because
it's an more eccentric ellipse than either planet's
orbit.

The Earth is already moving at 29.8 km/s, so
to leave Earth for Mars requires only that you
speed up less than 3 km/s. If you've timed it right
(the launch window we hear about), you're then
moving 2.7 km/s too slow when you get to Mars,
so you have to speed up that much to match in
with Mars' orbital velocity and start to fall in to
the Martian atmosphere (or maybe you just get
run over by Mars as you pass).

Those figures are only true if you start from
a co-moving point with the Earth. If you started
from the surface of the Earth and blasted off for
Mars all in one sustained flight, it would take
11.6 km/s to leave Earth and 5.7 km/s to land
on your tail jets on Mars, just the way they do
in the movies. But meteorites don't do that.

The key is that you have to speed up to fall out.
Being blasted off a planet usually involves some
considerable speeding up, I imagine.

But to "fall in" to a cotangential orbit shaped so
that it would just kiss the orbit of Venus needs you
to SLOW DOWN by 2.5 km/s in order to "fall in"
and when you arrive at Venus, you need to slow
down AGAIN, by 2.7 km/s, a total change of 5.2
km/s, ALL of it by slowing down.

To get from an outer planet to an inner planet,
you have to lose speed at both ends. Losing speed
on arrival is easy; all you have to do is smack into
the planet as asteroids are wont to do. But how
do you get blasted off a planet and then slow down
so to fall inward? Slowing down is hard to do in
a vacuum if you're not a rocketship.

When you escape the Earth, you're already moving
too fast to get to Venus. OK, yes, there are ways ---
odd elliptical orbits that will eventually intersect
with an inner planet's orbit. But, given a broad range
of ejection velocities and directions, a lot more stuff
goes out than in. It's true of all outer-inner transfers
wherever they start from.

Since it's harder to fall in than to fall out, there should
be more Earthites on Mars than there are Marsites on
Earth, more Mercuryites on Earth than Earthites on
Mercury, more Venusites on Earth than Earthites on
Venus, and so forth.

A clear example of how counter-intuitive the whole thing
is? Brett Gladman's numerical simulations of tens of
thousands of "particles" blasted off Mercury shows a
small but countable number ending up on Saturn's
moon Titan.

That's one heck of a trip and sounds improbable. But
"falling out" helps make it happen.


Sterling K. Webb
--------------------------------------------------------------------------
----- Original Message -----
From: <almitt2 at localnet.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Friday, August 26, 2011 12:25 AM
Subject: Re: [meteorite-list] Earth Ejecta Could Have Seeded Life on
Europa


> Hi Bernd and all,
>
> Easier or harder?? Takes less energy to fall in than out. Best!!
>
> --AL Mitterling
>
> Quoting "Bernd V. Pauli" <bernd.pauli at paulinet.de>:
>
>> Eric W. wrote:
>>
>> "Absolutely! Why not? It makes perfect sense."
>>
>> Well, Eric and List, because getting ejected into the outer reaches
>> of the solar system and surviving this "torture" is much easier than
>> "falling" toward the Sun without being "swallowed" by our central
>> star ... thinking of sungrazing comets ...
>>
>> Cheers,
>>
>> Bernd
>>
>>
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Received on Fri 26 Aug 2011 11:36:17 PM PDT