[meteorite-list] Astronomers Find Extrasolar Planet Heavyweight Champ

[Sterling K. Webb]

Hi, List,

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

Sterling K. Webb
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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."