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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 25 Apr 2007 05:11:25 -0500
Message-ID: <082e01c78722$1628a9f0$862e4842_at_ATARIENGINE>

Hi, Mark, List,

> would have been through hell in the
> past, (since the star is now a dwarf)

    A red dwarf is a main sequence star: once
a dwarf, always a dwarf. It's just a low-mass
star with a longer lifetime (25 billion years?)
than our Sun (10 billion years?). At a third
of a solar mass, it's got a respectable little
"heliosphere" and all the usual solar (or stellar)
apparatus, just less extensive than a G0 dwarf
star like us. But it doesn't have as big a system
to fend outside radiation away from. In general,
M-class star systems seem to be quiet places.
Some theorists regard smaller stars as safer
places (sort of like being a stellar mouse;
just keep quiet and no one will notice you).
M-class dwarfs are very, very common and
often very old, but their age is often hard to
determine. [Their stellar atmosphere is full of
diatomic molecules and their spectra are, like,
scrambled eggs!]
    
    Since I wrote my first post, I've looked
for information on the star itself, Gliese 581:
http://www.solstation.com/stars/gl581.htm
    "Gliese 581 is a cool and dim, main sequence
red dwarf (M2.5 V). The star has almost a third
(31 +/- 2 percent) of Sol's mass, possibly 29
percent of its diameter, and a bit more than one
percent (around 0.013) of its visual luminosity..."

    This means the sunlight there is "only" twice
as bright as sunlight here on Earth. (I'm still taking
the sunglasses.) Accounting for all the factors,
the solar energy at the planet should be about twice
the Earth's also.

    The composition of the Super Earth may be
different, too. "The star appears to be only
around 47 to 56 percent as enriched as Sol in
elements heavier than hydrogen ("metals")...
Its kinematic characterisitcs, magnetic activity,
and sub-Solar metallicity indicate that Gliese
581 is at least two billion years old. Gliese 851
is a variable star with the designation HO Librae."

    I don't like that "variable" part, do you?

    The earlier discovered planet is a "hot"
Neptune closer in to the star, with an estimated
temperature about like Venus. The not-so-standard
theory would be that this system formed so
slowly that the big one spiraled in because the
nebula stayed dusty and exerted drag on it. This
slow formation suggests a small nebula producing
a small star. But there's always plenty left over
for planets!

    Humorously, the authoritative website I just
quoted says the larger planet "would have
disturbed the development and orbit of a nearby
earth-type in the habitable zone..."

    Well, we all make wrong guesses, don't we?

    With its gravity, Gliese 581c can hold its
atmosphere against the weaker "solar" wind
of Gliese 581. Wouldn't be surprised to learn
it could capture and hold small amounts of
hydrogen and helium, too.

    Since it is likely to be more active tectonically,
there should be plenty of outgassing, but since
all the volatiles are released into the oceans rather
than the atmosphere, I would expect a carbonated
and suphurated ocean to pass dissolved gasses
into the atmosphere at a good clip.

    In other words, I would guess a dense
atmosphere with most of the thermo-regulation
coming from the balances of evaporation versus
cloud cover.

    Of course, I'm basing everything on averages.
What if it was volatile poor? Less oceans, maybe.
If it had half the water you'd expect, there would
be some land above water, not a lot, but some.
Maybe tectonics would build large continental
shelves around the land. Maybe that would be
a good place for life to evolve. (Seems to have
worked here!)

    Of course, if the star has less heavy elements
than the Sun, that suggests MORE volatiles rather
than less. Of course, in our ignorance, it may mean
that the planets of "metal-poor" stars leave more metals
in the zone of planetary formation. We don't really
know, having only one lousy solar system to examine.

    For decades, we've speculated about Earth-like
worlds close in to small M-class stars. Gliese 581c
is the first and closest thing to that we've actually
got evidence of. And it's next door, only 20 years
away by lightmobile...

    Anybody got a lightmobile? (I'll chip in for the gas.)


Sterling K. Webb
-------------------------------------------------------------
----- Original Message -----
From: "mark ford" <markf at ssl.gb.com>
To: <Meteorite-list at meteoritecentral.com>
Sent: Wednesday, April 25, 2007 3:10 AM
Subject: Re: [meteorite-list] Scientists find most Earth-like planet yet


Hi Sterling!

Nice assessment of Gliese 581c!

Interesting to further speculate: I wonder what else would the fact
that Gliese 581 (the star) is a 'red dwarf' bring to the party? (Apart
from the sunlight being further into the red, which is a good point),
but would a red dwarf mean there is essentially higher cosmic radiation
(since it's is a lot closer than us in comparison), maybe its also
bombarded by solar activity since it's nearer which could actually strip
its atmosphere, so it could potentially be a Mars like world, once wet
but now essentially a vacuum.

Additionally It's 'solar system' would have been through hell in the
past, (since the star is now a dwarf) so presumably there could be
massive amounts of bits debris-material hitting it, maybe caused by the
partial destruction of whatever other planets there where (apart from
the surviving hot Neptune et al)?!

Certainly an important discovery...


Best
Mark Ford






-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of
Sterling K. Webb
Sent: 25 April 2007 06:15
To: cynapse at charter.net; meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] Scientists find most Earth-like planet yet

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
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Received on Wed 25 Apr 2007 06:11:25 AM PDT