[meteorite-list] ODD PLANET

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri Sep 15 02:43:49 2006
Message-ID: <008901c6d892$492c1b50$5de18c46_at_ATARIENGINE>

Hi,


    Time was, every discovery of an extra-solar planet
was big news. Now, with the total pushing up toward
or past 200, it's like, ho-hum, another exotic planet,
unless it's was the smallest yet discovered or the
biggest or the hotest...

    But the new extra solar planet announced today is the
ODDEST. 450 light years away in the constellation of
Lacerta is a planet with a radius 1.38 times that of Jupiter,
or a diameter 1.76 times Jupiter, if you like, but it's
something that is, well impossible.

    Impossible, not odd, because Jupiter is, or was, believed
to be just about as big as a planet could get. Add more
mass and the planet would just compress more, get denser,
but remain almost the same size, only growing by tiny
increments, no matter how much matter you added to it!

    Eventually, if you added enough matter, when it was about
13 times the mass of Jupiter, deuterium in the core would
start to fuse and it wouldn't be a planet any more; it would be
a very small star, all without getting any bigger. So, theoretically,
it's impossible for a planet to be much bigger than Jupiter until
it becomes a brown dwarf star. In fact, theory says that if a
gas giant reached 13 Jupiter masses and turned into a faint star,
it would only be 90% of the size of this planet.

    Meet HAT-P-1. Not only is it 38% bigger than Jupiter; it
only weighs half of what Jupiter does. Not 13 times of what
Jupiter weighs, but only half. That makes HAT-P-1's density
only 0.19 that of water. That's lighter than a cork. A cork cork,
that is, like a wine bottle cork. That's a real problem for planet
theoreticians. Making it all out of the lightest element, hydrogen,
doesn't help; Jupiter is mostly hydrogen. Making it out of
cork is even worse...

    HAT-P-1 orbits very close to its star, going around every
4.5 days. The star ADS16402 is one of a double star system,
and a very ordinary star, similar to the Sun and about 3.6 billion
years old. It's bright enough you can see it (the star) with just
binoculars, they say.

    Ideas leap to mind. Maybe the heat from the star expands the
gas. Time for head scratching (and computer models). It turns out
that heat from the outside won't do it; the only way to puff up a
planet is to heat it from the inside. Maybe it's tidal force from
the star squeezing a tilted planet as it rotates. Computer says no,
or at least unlikely without extreme orbital eccentricity, and there's
no indication of that.

    It also turns out that an earlier extra-solar planet is too big
for theory: HD209458b. Not as big as HAT-P-1, but too big.
Everybody ignored it, figuring it was just a fluke, but two too-
big, too-light stars are too-many.

    Since this is two planets out of only eleven detected transiting
discoveries, it's obvious that the puffing-up mechanism isn't some
rare and exotic situation but something that happens 18% of the
time. But, at this point, we have not the foggiest notion of what
could do this to a planet.

    How would you puff up a planet like breakfast food?


Sterling K. Webb
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Read more:
http://www.sciencedaily.com/releases/2006/09/060914135220.htm
http://www.newscientistspace.com/article/dn10075-puffedup-planet-puzzles-astronomers.html
http://www.space.com/scienceastronomy/060914_cork_planet.html

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Received on Fri 15 Sep 2006 02:43:42 AM PDT