[meteorite-list] Scientists find most Earth-like planet yet

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 25 Apr 2007 15:32:17 -0500
Message-ID: <085101c78778$d2504650$862e4842_at_ATARIENGINE>

Hi, Paul, List,

> What necromancy
> produced that result?

    Some pieces of magic called the inverse square law,
Mr. Kepler's laws, and the mass-luminosity rule for stars,
a little data, and small human stepwise reasoning.

    We "know" the mass of the planet from the strength
of the effect by which we detected the planet. We
"know" the mass of the star from the mass-luminosity
rule. We "know" the period of the planet's orbit from
the periodicity of the observation.

    From the mass of star and period of orbit, Kepler
shows us we can derive the distance from the star
(semi-major axis). Now that we know the distance
of the planet from the star, we can calculate how much
of the star's energy falls on the planet.

    The remaining question is: how much of that energy
is absorbed by the planet and how much is reflected
away again. The answer, obviously, is somewhere
between a reflectivity of 0% and 100%!

    We can assume that the planet is what physicists
call a "black ball" whose "blackness" can vary from
pure black (all energy absorbed) to pure white (all
energy reflected away).

    The reason the discovers said that its "temperature"
is between 0 C and 40 C is not that has a climate! No,
if it's a perfect reflector, it's at 0 C. And if it's a perfect
absorber, it's at 40 C.

    If we perform the same naive calculation for our
dear little home world, pretending we don't know anything
about it, we get a temperature range that is somewhat lower
than Earthly reality. Why?

    Atmosphere! Our atmosphere traps infrared radiation
trying to escape and heats the whole planet up some.
There is always more infrared radiation trying to escape
than entered in the first place, because other frequencies
degrade to weaker infrared photons after bouncing around
reflecting off the planetary surface. This is true no manner
what the planet is like.

    All atmospheres of sufficient density are planet heaters.
The Earth must have had its reasonably dense atmosphere
throughout all of its history, because without it, the planet
would have quickly evolved into an irreversible Iceball
billions of years ago, a very frigid world with all the
oceans covered by hundreds of meters of ice and all
the land covered with snow and ice, and highly reflective
enough (90%+) to stay that way forever (unless vulcanism
could restore a warming atmosphere eventually). We've had
brushes with that outcome (go Google "snowball earth").

    Back to the data. Since Gliese 581c is five Earth masses,
it has more than enough gravity to hold on to gasses and
volatiles. Look at what a good job Venus does of retaining
atmosphere! Too dam much of a good job -- if Venus
had no atmosphere at all, it would be a lot cooler that it is.

    We don't really know what mix of materials existed in
the dust/gas cloud the Gliese 581 system formed from.
We assume -- it's called the Copernican Principle -- that
it wasn't all that different from our system or any other
star system in the neighborhood or the rest of the Galaxy.
We assume that we're typical, not special. We assume
that Gliese 581 is typical, not special.

> composition of the atmosphere is critical
> to knowing the temperature of the planet -
> think Venus vs. Mars

    I know global warming is all the rage these days, but
the real critical difference is how much energy from
the Sun the planet receives! Venus gets 4.7 times more
energy per square unit than Mars because of their
respective distances from the Sun. That's most of the
difference.

    Both have unique problems, too. Mars has enough
gravity to hold onto a much thicker atmosphere than
it presently has. The evidence of past liquid water
erosion shows it has to have had a much thicker
atmosphere in the past. All those volatiles and no
atmosphere? Hence, we have a lot of theories about
Mars' atmosphere being "eroded" away.

    Venus appears to have absolutely no volatiles on
its surface, yet it has this killer atmosphere (and I
do mean "killer"). How can a planet with no volatiles
generally have a superabundance of one and only one
volatile -- carbon dioxide? Venus has more CO2
in its atmosphere than could be produced by oxidizing
the entire surface carbonate inventory of the Earth!
Something really nasty happened to Venus...

    Certainly, we can't "know" what the planet
Gliese 581c is really like. We CAN guess the most
likely, most "average," most common planetary
outcome for a body this size this distance from
this star would be. Yes, Gliese 581c could be
an oddball. But that would be... odd.



Sterling K. Webb
---------------------------------------------------------------------------
----- Original Message -----
From: <valparint at aol.com>
To: <Meteorite-list at meteoritecentral.com>
Sent: Wednesday, April 25, 2007 7:29 AM
Subject: [meteorite-list] Scientists find most Earth-like planet yet


My BS detector is buzzing like crazy. "They have not directly seen the
planet" but somehow know that it has "balmy temperatures." What necromancy
produced that result?

The composition of the atmosphere is critical to knowing the temperature
of the planet - think Venus vs. Mars. If they didn't directly see the
planet there is no way they can know anything about its atmosphere.

Paul Swartz

>European astronomers have spotted what they say is the
>most Earth-like planet yet outside our solar system, with balmy
>temperatures
>that could support water and, potentially, life.
>
>They have not directly seen the planet, orbiting a red dwarf star called
>Gliese
>581. But measurements of the star suggest that a planet not much larger
>than the
>Earth is pulling on it, the researchers say in a letter to the editor of
>the
>journal Astronomy and Astrophysics.

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Received on Wed 25 Apr 2007 04:32:17 PM PDT