[meteorite-list] Martian Meteorite Heat Ablation?

From: Martin Altmann <altmann_at_meteoritecentral.com>
Date: Thu, 9 Aug 2007 09:31:21 +0200
Message-ID: <01f201c7da57$4c5b24c0$177f2a59_at_name86d88d87e2>

Hi there,

I remember that one of the probes took by chance a picture of a meteor in
the Martian sky, does anyone remember the link to the picture?

Martin

-----Urspr?ngliche Nachricht-----
Von: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von Chris
Peterson
Gesendet: Mittwoch, 8. August 2007 23:45
An: Meteorite List
Betreff: Re: [meteorite-list] Martian Meteorite Heat Ablation?

Thanks for that analysis (and to Larry). I didn't really give it much
thought before posting. It's interesting the number of things that scale
unexpectedly with changes in gravitational potential.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: "Meteorite List" <meteorite-list at meteoritecentral.com>
Cc: "Chris Peterson" <clp at alumni.caltech.edu>
Sent: Wednesday, August 08, 2007 2:41 PM
Subject: Re: [meteorite-list] Martian Meteorite Heat Ablation?


Hi, Chris, and List,

> Presumably, meteors begin burning somewhat
> lower on Mars, and have a greater chance of reaching
> the surface...

    The rate at which pressure declines with altitude is
characterized by the scale height, the altitude at which
pressure has dropped by a factor of "e" (nat. log. base =
2.72forever). The scale height of the Martian atmosphere
is about 11 kilometers; for the Earth it's only about 6
kilometers.

    The formula for the scale height is H = ( k * T ) / ( M * g ),
where k = Gas constant = 8.314 J?(mole K)^-1, T = mean
planetary surface temperature in kelvin degrees, M = mean
molecular mass of dry air (units kg?molec ^-1), g = acceleration
due to gravity on planetary surface.

    Molecular mass of the Martian atmosphere is about 50%
greater then the Earth's "M," but "g" is 38% of the Earth's.
Planets with lower gravity have "taller" atmospheres, if you
want to remember it the easy way. There are always "wrinkles"
to ideal gas formulas. At very high altitudes, the "air" is so
thin that diffusion is easy, so every species of gas molecule
has "its own" scale height. But Mars is mostly carbon dioxide,
so that doesn't change things much.

    Atmospheric pressure on the surface of Mars varies from
around 30 Pascals on Olympus Mons to over 1155 Pascals
in the depths of Hellas Planitia, with a mean surface level pressure
of 600 Pascals. This is less than 1% of the surface pressure on
Earth (101,300 Pascals). The equivalent pressure in the atmospheres
of the two planets can be found in Mars' thin atmosphere at a
height of 35 km above either planet's surface.

    Another implication for the case of a meteorite entry is that
the Martian atmosphere at 60 to 80 kilometers above the surface
is DENSER than the atmosphere of the Earth at that height. All
Martian densities at altitudes above 34 kilometers are, due to the
fact that the pressure (hence density, since the pressure of a
planetary atmosphere is a function of its mass) falls off less
steeply than is the case in the Earth's atmosphere.

    So, the meteoroid that "lights up" at 60 km in the Earth's
atmosphere, will presumably "light up" at a higher altitude in
the Martian atmosphere. It may very well terminate its ablative
flight at a higher altitude (if that happens above 34 kilometers)
or a lower altitude (if that happens above 34 kilometers) than
it would in the Earth's atmosphere, and have a correspondingly
longer or shorter "dark fall" (but a much slower fall due to the
lesser Martian gravity).

    Ouch! It's hard to think outside your own gravity well! Now,
I'm going to hand the calculator back to Chris...


Sterling K. Webb

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Received on Thu 09 Aug 2007 03:31:21 AM PDT