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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 25 Apr 2007 00:15:10 -0500
Message-ID: <081301c786f8$b375ed50$862e4842_at_ATARIENGINE>

Hi, All,

    In our fast moving world, Gliese 581 and its
new planet already have a Wikipedia entry!
http://en.wikipedia.org/wiki/Gliese_581

    There is another planet, a close hot "Neptune"
discovered earlier and they're pretty sure there's a
third planet further out. The bigger planet also has
a Wiki:
http://en.wikipedia.org/wiki/Gliese_581_b

    It's just like show business: yesterday, you were
a nobody and today, you're a Star!

    Gliese 581 is about 1/3rd of the mass of the Sun,
which means that it is only 0.037 the luminosity of
the Sun, a mere 3.7%. Gliese 581 is a neighbor, only
20.4 light years away, one of the 100 closest stars.

    The newly discovered planet is 0.073 AU from
the star, about 11,000,000 kilometers, and takes
only 12.91 days, or 310 hours, to orbit its star.

    If it seems to you that it must be rather dim on
Gliese 581c, with a star only 3.7% of the brightness
of the Sun... think again! At 0.073 AU, a star is 187.5
times brighter than it is at 1.0 AU, so it's fortunate
that the star is only 3.7% of the brightness of our
Sun, because "sunlight" on Gliese 581c is a mere
6.95 times BRIGHTER than sunlight on Earth.

    See, we already know something about space
travel to Gliese 581c! Take Sunglasses!!

    My guess is that Gliese 581c is likely at the
warmer end of that temperature estimate of 0 degrees
to 40 degrees. Even though the brightness is 6.95
times brighter than Earth, this is weak red light, not
hot buttery yellow sunlight like Earth. Those red
photons just don't pack the punch...

    At 5 times the mass of the Earth, Gliese 581c is
a Super Earth. What would a Super Earth be like?
All we can assume is that it will be made out of
roughly the same elements in roughly the same
proportions as our own Earth, which may not be
true at all, but it's a starting point (and an assumption
we make about our own solar system en toto).

    If you start with the same recipe mix of ingredients
as the Earth and just made a bigger batch of planet
(five boxes of Earth Mix), is it just the same as the
Earth, only more so? Nope, more of the same is
definitely not the same.

    If the Earth were bigger, the volume of water would
increase faster than the increase in surface area, so the
oceans would be deeper. Because of the deeper
oceans and the greater gravity, the pressures at the
bottoms of those oceans would be much higher.

    Continents and their mountains would be much
lower, because the temperatures in the crust would
increase faster with depth, until the fluid point would
be reached in the crust instead of the mantle like it is
on "our" Earth. Mountains can only pile up until the
pressures under them are about 3000 to 3500
atmospheres, and that zone would be reached at
shallower and shallower depths on a bigger and
bigger Earth.

    Since the solid crust of a larger "Earth" would be
much thinner, heat transfer to the surface much faster,
vulcanism much livelier, plate tectonics much zippier.

    Gliese 581c will have a 2.25 times the surface area
of the Earth, 3.375 times the volume of the Earth, a
density of about 8.0 gm/cm^3, and a surface gravity
2.2 times greater than the Earth's (Note to Self: take
support hose as well as sunglasses).

    Because it would have 5 times the water but only
2.25 times the surface, the average ocean depth would
be about 6700 meters! The pressure at the depths of
these oceans would be about 2200 atmospheres. The
highest mountains possible would be about 5000 meters
(calculating from the median diameter), so if you were
the greatest mountain climber on Gliese 581c, standing
on the top of Gliese 581c's highest mountain, you would
have 1500 meters of water above you!

    Whoops! No continents. Gliese 581c must be a
WaterWorld! With a world-wide ocean in free circulation,
it is likely that temperatures are fairly uniform over the
planet, without great differences between the climate
of the equator and the poles, whatever the inclination
of Gliese 581c's axis.

    On our Earth, the crust is about 30 kilometers thick, but
the lithosphere (rocks that stay stiff and not slushy and
slippy) is about 75 kilometers, so the Earth's lithosphere
contains all the crust and the top part of the mantle.

    The crust of Gliese 581c would be about 70 km
thick, but the lithosphere would only be about 50 kilometers
thick. This means that it would be very difficult to sink
pieces of crust (by subduction) and equally difficult to
bring deep basalt magmas to the surface, and the upper
lithosphere is probably impoverished in iron-rich and
silica-poor rock types.

    On the other hand, Gliese 581c's silicate crust would be
recycled very rapidly with lots of local vulcanism and
"hotspots" and have a very similar composition everywhere.
The only weathering that would be possible would be
chemical, because all the volatiles are released into the
oceans rather than the atmosphere. Any "continental"
rises would be underwater.

    So a bigger Earth is not just a bigger Earth. Knowing
that somebody will ask how big a bigger Earth has to be
before there's no land at all, just oceans, the answer is:
somewhere between 2-1/2 and 3 Earth masses is the
point where the median ocean depths equal the height
of the highest possible mountain. At a mass of 5 Earths,
the surface of Gliese 581c is almost certain to be ocean,
100% water. And at 2.2 gravities, wave heights would
be less than half those of the Earth's ocean.

    So, to summarize Gliese 581c: sunglasses, bulky
support hose, and lousy surfing.



Sterling K. Webb
-------------------------------------------------------------------
----- Original Message -----
From: "Darren Garrison" <cynapse at charter.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, April 24, 2007 10:44 PM
Subject: [meteorite-list] Scientists find most Earth-like planet yet


http://www.cnn.com/2007/TECH/space/04/24/exoplanet.reut/index.html

WASHINGTON (Reuters) -- 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.

"This one is the first one that is at the same time probably rocky, with
water,
and in a zone close to the star where the water could exist in liquid form,"
said Stephane Udry of the Geneva Observatory in Switzerland, who led the
study.

"We have estimated that the mean temperature of this super-Earth lies
between 0
and 40 degrees Celsius, and water would thus be liquid."

Most of the 200 or so planets that have been spotted outside this solar
system
have been gas giants like Jupiter. But this one is small.

"Its radius should be only 1.5 times the Earth's radius, and models predict
that
the planet should be either rocky, like our Earth, or covered with oceans,"
Udry
said in a telephone interview.

It appears to have a mass five times that of Earth's.

The research team includes scientists credited with the first widely
accepted
discovery of a planet outside our solar system, in 1995.

Many teams are looking for planets circling other stars. They are especially
looking for those similar to our own, planets that could support life.

That means finding water.

X marks the spot
"Because of its temperature and relative proximity, this planet will most
probably be a very important target of the future space missions dedicated
to
the search for extra-terrestrial life," Xavier Delfosse, a member of the
team
from Grenoble University in France, said in a statement.

"On the treasure map of the universe, one would be tempted to mark this
planet
with an X."

Gliese 581 is among the 100 closest stars to Earth, just 20.5 light-years
away
in the constellation Libra.

A light-year is the distance light travels in a year, about 6 trillion miles
(10
trillion km).

It is smaller and dimmer than the sun, so the planet can be close to it and
yet
not be overheated.

"These low-mass stars are the ones where we are going to be able to discover
planets in the habitable zone first," said planet-hunter David Bennett of
the
University of Notre Dame in Indiana, who was not involved in the research.

Bennett cautioned that current temperature alone does not mean water still
exists on the planet. It could have burned off ages ago, when the star was
hotter than it is now.

Udry's team uses a method known as radial velocity, using the European
Southern
Observatory telescope at La Silla, Chile.

The same team has identified one larger planet orbiting Gliese 581 already
and
say they have strong evidence of a third planet with a mass about eight
times
that of the Earth.

Future missions, perhaps in 20 to 30 years, may be able to block the light
from
the star and take a spectrographic image of the planets. The color of the
light
coming from the planet can give hints of whether water, or perhaps large
amounts
of plant life, exist there.
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Received on Wed 25 Apr 2007 01:15:10 AM PDT