'Backward' planet has density of foam coffee cups
Contrary to a recent TV cell phone ad, Dunkin' Donuts isn't likely to
set up shop in space any time soon.
But if it did, the donut chain might like to build next to WASP-17b,
a newfound planet that's puffed up to be roughly as dense as a foam
coffee cup.
An artist’s illustration shows a Jupiter-like planet orbiting
near its host star. At about twice as wide as Jupiter, the
newfound planet WASP-17b is one of the largest and least dense
worlds yet found, astronomers announced in August 2009.
Illustration courtesy NASA/Hubble. |
WASP-17b orbits a star about a thousand light-years away. In addition
to its exceptionally low density, the planet is one of the largest yet
found. "When I first saw that this thing might have a radius twice that
of Jupiter, I was really astounded", said David Anderson of Keele
University, a member of the UK-based Wide Area Search for Planets (WASP)
consortium.
WASP-17b probably got so big because of its unusual orbit, Anderson
and colleagues say in a new paper describing the find.
The planet is also the first found to orbit 'backward' around its
star, an eccentricity likely caused by a collision with a larger
neighbor early in WASP-17b's life. That planetary crash may have nudged
WASP-17b into an elongated orbit, which led to variations in the
gravitational pull exerted on the planet by its host star, Anderson
said.
Changes in the star's pull would have generated powerful tidal
forces, which in turn would have created friction that got dissipated as
heat. The planet's heated gases would have then expanded, causing the
world to bloat.
But the astronomers haven't conclusively proven that WASP-17b has an
eccentric orbit, Anderson said, and tidal forces aren't the only
possible explanation for the planet's swollen size. The gas giant could
have expanded in a similar fashion, he noted, if the planet's early
atmosphere was opaque enough to trap the right amount of heat from its
star.
National Geographic News |