[meteorite-list] extrasolar planet with ginormous rocky core

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Fri Jul 1 02:23:54 2005
Message-ID: <42C4E154.C3052ED4_at_bhil.com>

Hi,

    One reason for the mixed reception of the discovery is the problem of where these giant planets are
found.

    Before any extrasolar planets were found, some theorists proposed that giant planets formed far out
in a young solar system, spiralling inward until they ran out of material.

    In this theory, Jupiter migrates inward until it gets to 5 AU where the already depleted asteroid
zone stops it. Saturn stops when it gets to the zones depleted by Jupiter ahead of it, and so forth.

    When extrasolar discoveries started pouring in, there were mostly big planets, in very close. This
was seen as a vindication of the spiral-in theory. These were systems where there was so much material
that the giant planets spiralled all the way to the star before they ran out of planet building juice.

    But, a giant rocky core suggests it formed in place. No spiralling?

    Of course, with the method used, big planets close in are the only detectable planets (at first)
because they have the strongest "signals" to be detected. It's another "observer" effect. The only
planets discovered are oddballs because they're the only detectable ones.

    This is why everyone says these detections mean there must be huge numbers of normal planets. We
assume there are far more "normal" ones everywhere, too.

    But that is true only if the oddballs are distributed randomly. If they're oddballs, they must be
essentially random events. So, how are the discoveries distributed?

    In ramdom distribution, if you find one within 10 ly (lightyear), you should find a total of 8 out
to 20 ly, a total of 27 out to 30 ly, a total of 64 out to 40 ly, a total of 125 out to 50 ly, well, you
get the picture, goes up by the cube of the search radius.

    In the more than 100 extrasolars discovered (a goodly number and statistically workable), here is
the pattern:
    One within 10 ly (lightyear), a total of 3 out to 20 ly, still a total of 3 (no new finds) out to 30
ly, a total of 6 out to 40 ly, a total of only 12 out to 50 ly.
    Then, suddenly, between 50 and 60 ly out, 12 more new worlds, doubling the previous total to 24!
    But between 60 and 70 ly out, only 4 more, between 70 and 80 ly out, only 2 more, then, between 80
and 90 ly out, 8 more, between 90 and 100 ly out, 9 more, between 100 and 110 ly out, 10 more, then,
between 110 and 120 ly out, 12 again!
    After that discoveries fall off and off. In each new 10 ly increase in search: 6, 8, 6, 6, 4, 4, 0,
3, 1, 1, 3, 0, 1, 1...

    Graph it (pictures always better) and you see a curve with two sharp peaks: one at 55 lightyears out
and a fatter one at twice that distance, 110 lightyears out. In the detection method used, distance does
NOT reduce observability, so that isn't the reason. (Planets have been found all the way out to 4900
lightyears!)

    This is SO FAR from resembling a "normal" distribution as to raise the ultimate scientific question:
WHAT IN THE BLUE-BLAZES HECK IS GOING ON HERE?!!

    Interestingly, a few years ago, every web site listing extrasolars' data (there are many) gave the
distance for each and every discovery, all of them. Now, NONE of them give ANY distances for ANY stars
with extrasolar planets. Hmmm.

    I had to look each star up individually to make a table of distances. It was work. I hate work. Why
did they make me do work?

    Oh, great intelligences of the List! I call upon you! What explains this distribution? From the
vasty deeps of your intellects, tell me! What creates oddball planet systems in spherical shells with
radii that are multiples of 55 lightyears? Huh?

    Anybody?


Sterling K. Webb
------------------------------
Darren Garrison wrote:

> http://www.msnbc.msn.com/id/8424348/
>
> Strange new world unlike any other
> Large solid core provides clue to how giant planets might form
>
> By Robert Roy Britt
>
> Updated: 8:44 p.m. ET June 30, 2005
> A strange newfound planet as massive as Saturn appears to have the largest solid core known,
> providing an important clue to how some giant planets might form and setting off a controversy over
> how it formed.
>
> The world passes in front of its host star, so even though they can't actually see the it,
> astronomers were able to glean important information about its size and density, and therefore infer
> things about its composition.
>
> Scientists who investigated the large and presumed rocky core of the planet say it supports the idea
> that giant planets can indeed form by gradual accumulation of a core, long the leading theory of
> planet formation but one that has been called into question lately.
>
> But how it grew such a massive core is beyond the ability of current theories to explain, according
> to one expert who does not agree that the isolated discovery proves anything.
>
> With the standard core accretion model, as it is called, dust around a newborn star gathers into
> clumps, which become asteroids, comets and protoplanets. Some grow large enough to form rocky worlds
> like Earth. The theory states that a giant planet like Jupiter is created in the same manner,
> reaching a critical point when its core is massive enough to attract a large envelope of gas.
>
> But the giant planets in our solar system don't have cores large enough to prove the idea. Other
> researchers have suggested that they might have formed, instead, by the sudden collapse of gas from
> a knot in the cloud of material that circles a new star.
>
> "For theorists, the discovery of a planet with such a large core is as important as the discovery of
> the first extrasolar planet around the star 51 Pegasus in 1995," said Shigeru Ida, theorist from the
> Tokyo Institute of Technology, Japan.
>
> The planet orbits a sun-like star called HD 149026.
>
> It is very close to the star, taking just 2.87 days to make a yearly orbit. That makes it hot --
> about 2,000 degrees Fahrenheit on the star-facing side. Modeling of the planet's structure shows it
> has a solid core approximately 70 times Earth's mass.
>
> The scientists don't believe the core could have formed by cloud collapse. They think it must have
> grown by accumulation of dust and rock, and then acquired gas.
>
> The finding does not rule out collapse as an alternate means of making planets. Astronomers don't
> know if there are multiple methods or not.
>
> "This is a confirmation of the core accretion theory for planet formation and evidence that planets
> of this kind should exist in abundance," said Greg Henry, an astronomer at Tennessee State
> University, Nashville. Henry detected the dimming of the star by the planet with robotic telescopes
> at Fairborn Observatory in Mount Hopkins, Arizona.
>
> Not so fast, says Alan Boss, a theorist at the Carnegie Institution of Washington who has championed
> the collapse model in recent years.
>
> "I have not seen any core accretion models that predict the formation of such a beast," Boss told
> SPACE.com. "I suspect that the core accretion folks will be scratching their heads for a while
> over how this thing could have formed."
>
> Since this planet is just one of about 150 that have been discovered beyond our solar system, Boss
> thinks its premature to claim core accretion has been proved.
>
> "I suspect that both disk instability and core accretion can occur, as well as intermediate, hybrid
> mechanisms," Boss said.
>
> The research was supported by NASA, the National Science Foundation and the National Astronomical
> Observatory of Japan. The discovery will be detailed in the Astrophysical Journal.
>
> ?? 2005 Space.com. All rights reserved. More from Space.com.
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Received on Fri 01 Jul 2005 02:23:16 AM PDT