[meteorite-list] Subject: Re: Habital Planet Discovery Announcement

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 1 Oct 2010 20:46:15 -0500
Message-ID: <B46A60066E4640B185A06A60C728EEFC_at_ATARIENGINE2>

Hi,

Larry is, as usual, completely correct. But there are
some rough indications. Dynamic studies show that
the system that exists is only dynamically stable if it
is co-planar. Meaning, the planets orbit at roughly the
same inclination, i.e., in the same plane.

So, assuming the system is co-planar, the next big
question is, do the planets transit the star? Many
attempts to observe transits have not found any.
So, presumably the orbital plane is tilted enough
to our line of sight that the planets don't cross the
star, when seen from here. But transits are very hard
to observe in a splotchy small M star.

The dynamic requirement of stability limits the maximum
and minimum masses. Earlier observations limited the
max to 1.6 times the minimum. These observations pin
it down further to a max of 1.4 times the min. More
observations will pin the range down further. Presently,
they say, the range is 3.1 E-masses to 4.3 E-masses.
http://arxiv.org/PS_cache/arxiv/pdf/1009/1009.5733v1.pdf
(This is the discovery paper.)

The size of the planet is entirely an estimate and (like
everything else) is not simple. They say: "the radius of
GJ 581g is expected to be 1.3 - 1.5R if homogeneous
and composed primarily of the perovskite phase of MgSiO3
(Earth-like), or 1.7 - 2R if water-ice. All radii are predicted
to be 20% smaller if the planet is differentiated, so the
planet is likely to have a radius below 1.5R. The mass and
radius estimates imply a surface gravity of 1.1 - 1.7 g,
very near that of the Earth."

Since Gliese 581 does not have the same mix of elements
as our own star, all these Earth-like assumptions have a
certain shakiness about them. The "solar nebula" of Gliese
581 has twice as much hydrogen and helium as heavier
elements relative to our nebular proportions. So, one COULD
assume that there would be more volatiles in the planets.

For a solar system to have more volatiles is a Gimme for
the formation of planets like Jupiter and Saturn, gas giants
which are mostly volatiles. Yet, Gliese 581 has NO gas giants.
There is no Jupiter, hot or cold, not even a lousy Saturn.
It has a Neptune (16 E-masses), but it's the closest planet
to the star. It could be a Jupiter that spiraled in due to
dust drag and got its volatiles boiled off.

It is entirely possible that Gliese 581 has, instead, a volatile-
poor solar system, that all of its planets are terrestrial and
short on volatiles. How could that happen? Well, in a nebula
with less heavy elements, accretion would proceed more
slowly which would give the newly active star time to blow the
forming volatiles away. At the worse, all these worlds, in all
the available sizes, could be rocky and airless. (That would
explain the absence of "Jupiters.")

Equally possible is that if accretion proceeded very quickly,
all the planets could have accreted in place and be very
volatile-rich, ranging from a shiny steam-atmosphered giant
to waterworlds to iceballs.

Neiyher one sounds so "habitable," does it?

But, if they DO have atmospheres, we can say with certainty
that any planet's potential Greenhouse Effect will be greater
than the Earth's! Class M stars emit a large amount of their
radiation in the infrared. As a result, since the greenhouse
effect works by absorbing infrared radiation, the surface
temperatures would be higher than that predicted by
modeling such a world as if it were the Earth.

More transit observations would pin things down better.
The search for transits is best done by many telescopes,
properly equipped, over a long period of time, to determine
the light curve precisely. Even amateurs can contribute
and make discovery observations. See this website:
http://www.transitsearch.org/

Conceivably, if the planets transit, we could try to look for
signatures for any atmosphere.

All the exact data for all the Gliese 581 planets and blanks
where we don't know:
http://exoplanet.eu/star.php?st=Gl+581&showPubli=yes&sortByDate

Discussion of what "habitable" might mean:
http://www.centauri-dreams.org/?p=14589

Another "good" discussion on what is meant by the statement
that the chance of life is "good."
http://www.universetoday.com/74679/could-chance-for-life-on-gliese-581g-actually-be-100/

Frankly, I have always thought that we have very little
business deciding what "habitable" means. The very term
suggests that WE could inhabit the place. The notion that
WE are the standard by which "life" should be judged is
highly suspicious to me. It sounds very much like our
former unjustified assumption that our planet was the
center of the entire universe.

Is there somewhere a team of alien astronomers going
over their data on exoplanets with disappointment and
crossing off the list of targets to pursue further a world
that's too small, too hot, too wet, and with a significant
amount of a poisonous gas in its atmosphere. They've
just eliminated the Earth.

It is very hard for us to conceive of life in any other
terms than that of the life we know. It's difficult not
to be a "carbon chauvinist," as Carl Sagan called it.
It's a very complex system that we know actually
works. If there is another complex system that works,
we wouldn't know how it could work, even if we could
imagine its basics.

As long as we know only one system of living things,
we lack all basis for judgment. There could be thousands
of forms of intelligent life in the galaxy, every one with a
different physical system. Or there could be thousands
of forms of intelligent life in the galaxy, every one made
out of carbon, hydrogen, oxygen and nitrogen, and run
by DNA instructions.

There is no way to calculate the odds of either one.


Sterling K. Webb
---------------------------------------------------------------------------------
----- Original Message -----
From: <lebofsky at lpl.arizona.edu>
To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
Cc: <countdeiro at earthlink.net>; <meteorite-list at meteoritecentral.com>
Sent: Friday, October 01, 2010 6:23 AM
Subject: Re: [meteorite-list] Subject: Re: Habital Planet Discovery
Announcement


> Hi Sterling:
>
> I hope that I am not repeating something. Too many emails on too many
> subjects (not all the metlist) the last few days and getting ready for
> a
> conference.
>
> One thing seems to be missing in these discussions; how the planets
> were
> detected.
>
> All of the planets in the Gliese 581 system were detected by
> spectroscopy.
> You look at a spectral line from the star and, over time it shifts to
> the
> blue and then to the red. This is the Doppler shift as the star moves
> toward and away from you (respectively) as it is tugged on by it
> companion
> planet. It take many orbits of the planet to verify this motion, not
> just
> one "signal." The bigger the planet, the more the spectral line
> shifts,
> the easier it is to see." The closer the planet is to the star, the
> shorter the cycle is and the easier it is to see (if the period is a
> year,
> it takes several years to see several cycles). This obviously gets
> very
> complicated when you have multiple planets and are looking for cycles
> on
> cycles.
>
> This leads to a very important thing that seems to be left out of all
> of
> these discussions.The numbers quoted are MINIMUM masses. The Doppler
> shift
> is the shift in the direction of the viewer. These numbers assume that
> the
> planet orbits are lined up with the Earth, which would be highly
> unlikely.
> For the Gliese planetary system, the inclination of the planets is not
> known. If their orbits are in reality tilted by say 45 degrees, their
> masses would be about 1.4 times the numbers quoted. Still not bad. The
> distance from the star is only dependent on the mass of the star and
> the
> distance of the planet from the star (Kepler's Law, orbital period),
> but
> the mass is dependent on the inclination of the orbits relative to the
> Earth.
>
> Again, I hope I am not repeating others on this.
>
> Larry
>
>> Not to doubt the scientific trustworthiness of
>> the Daily Mail, but they state that the light pulse
>> was seen December, 2008, "long before it was
>> announced that the star Gliese 581 has habitable
>> planets in orbit around it."
>>
>> But Gliese 581 c, the first low mass extrasolar
>> planet found to be near its star's habitable zone,
>> was discovered in April 2007, and Gliese 581 b,
>> approximately Neptune-sized and the first planet
>> detected around Gliese 581, was discovered in
>> August 2005.
>>
>> Discovered at the same time as Gliese 581 c, a third
>> planet, Gliese 581 d, has a mass of roughly 7 Earths,
>> or half a Uranus, and an orbit of 66.8 Earth days. It
>> orbits just within the outer limit of the habitable zone.
>>
>> The fourth planet, Gliese 581 e, was announced on
>> 21 April 2009. This planet, at an estimated minimum
>> mass of 1.9 Earths, is currently the lowest mass exoplanet
>> identified around a "normal star." The more distant
>> Gliese 581 f was found at the same time.
>>
>> Gliese 581 was much in the news by December, 2008.
>> It was known that there were low-mass planets and that
>> there were planets in the habitable zone. The BEBO
>> message had been "sent" just two months before, in
>> October, 2008.
>>
>> It is certainly not true that the pulse was "long before it was
>> announced that the star Gliese 581 has habitable planets
>> in orbit around it." It was well known.
>>
>> Unrepeated signals don't count. Basic rule of SETI.
>>
>>
>> Sterling K. Webb
>> --------------------------------------------------------------------------
>> ----- Original Message -----
>> From: <countdeiro at earthlink.net>
>> To: <meteorite-list at meteoritecentral.com>
>> Sent: Thursday, September 30, 2010 10:40 PM
>> Subject: [meteorite-list] Subject: Re: Habital Planet Discovery
>> Announcement
>>
>>
>>> Listees,
>>>
>>> And now we have this to contemplate.
>>>
>>> http://www.dailymail.co.uk/sciencetech/article-1316538/Gliese-581g-mystery-Scientist-spotted-mysterious-pulse-light-direction-newEarth-planet-year.html
>>>
>>> Best to all,
>>>
>>> Count Deiro
>>> IMCA 3536
>>> ______________________________________________
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>>
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>
>
Received on Fri 01 Oct 2010 09:46:15 PM PDT