[meteorite-list] Astronomers Find Extrasolar Planet Heavyweight Champ

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 2 May 2007 12:55:57 -0500
Message-ID: <0b0f01c78ce3$23e2a7f0$f54de146_at_ATARIENGINE>

Hi, List,

    Last week, the lightest extrasolar planet;
this week, the heaviest!

Sterling K. Webb
---------------------------------------------------

http://www.space.com/scienceastronomy/070502_supermassive_planet.html

Astronomers Find Extrasolar Planet Heavyweight Champ
By Tariq Malik
Staff Writer

Astronomers have found the heavyweight champion
of extrasolar planets in the form of an odd alien
world slightly bigger than Jupiter, but more than
eight times as massive.

Dubbed HAT-P-2b, the super-dense planet is the
most massive known to transit across its parent
star, but the weirdness doesn't stop there.
Its oval orbit is so extreme that it first
bakes the planet, and then cools it off during
an annual trip that takes just more than five days.

"This planet is so unusual that at first we
thought it was a false alarm--something that
appeared to be a planet but wasn't," said
astronomer Gaspar Bakos, who led the team
at the Harvard-Smithsonian Center for
Astrophysics. "But we eliminated every
other possibility, so we knew we had a
really weird planet."

The planet is a gas giant in orbit around
the star HD 147506, which is about twice
the size of our own Sun and burns a bit
hotter in a system 440 light-years from
Earth in the constellation Hercules.
Bakos and his colleagues used a series
of small automated telescopes known as
the HATNet to discover the planet. Their
findings are detailed in a paper submitted
Tuesday to the Astrophysical Journal.

One weird world

Astronomers have found about 230 extrasolar
planets beyond our own solar system, and
last week announced the discovery of an
Earth-like planet could support liquid water.

Every five days and 15 hours--the time it
takes the planet to complete a full trip
around its star--HAT-P-2b crosses in front
of its stellar parent, as seen from Earth,
in what astronomers call a transit. During
such transits, researchers can determine the
physical size of extrasolar planets by
measuring how much they dim the light of
their central star.

Bakos and his team found that the newly
discovered planet is about 1.18 times
brighter than Jupiter and 8.2 times as
massive. A 150-pound (60-kilogram) person
on Earth would weigh 2,100 pounds (952
kilograms), or just over one ton, and
experience about 14 times Earth's gravity
at the visible cloud top surface of
HAT-P-2b, researchers said.

The planet's extremely elliptical orbit
brings it within about 3.1 million miles
(4.9 million kilometers) of its parent
star on the inside, and swings out to a
distance of about 9.6 million miles
(15.4 million kilometers). For comparison,
Earth orbits the Sun at a distance of
about 93 million miles (150 million
kilometers), but would range between
the orbits of Mercury and Mars if its
orbital path mimicked the extremes of
HAT-P-2b.

Eccentricity explained

Astronomers believe that the odd eccentricity
of the planet's orbit--all previous extrasolar
worlds found via the transit method have
circular orbits--may be due to another,
outer world whose gravitational pull
disturbs the path of HAT-P-2b.

If the planet contained about 50 percent
more mass, it could have fired up nuclear
fusion and burn as a star for a short while,
researchers added.

"HAT-P-2b is hot, but it's not a Jupiter,"
CfA astronomer Robert Noyes, a co-author on
the study, said, adding that previous planets
found via the transit method have been billed
as 'hot Jupiters.' "It's much denser than a
Jupiter-like planet; in fact, it is as dense
as Earth even though it's mostly made of
hydrogen."
Received on Wed 02 May 2007 01:55:57 PM PDT