 the planet contains about 8.2 times Jupiter's mass. A person who weighs 150 pounds on Earth would tip the scale at 2100 pounds, and experience 14 times Earth's gravity, by standing on the visible surface (cloud tops) of HAT-P-2b.
CfA astronomer and co-author Robert Noyes said, "All the other known transiting planets are like 'hot Jupiters.' HAT-P-2b is hot, but it's not a Jupiter. 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."
"This object is close to the boundary between a star and a planet," said Harvard co-author Dimitar Sasselov. "With 50 percent more mass, it could have begun nuclear fusion for a short time."
An intriguing feature of HAT-P-2b is its highly eccentric (e=0.5) orbit. Gravitational forces between star and planet tend to circularize the orbit of a close-in planet. There is no other planet known with such an eccentric, close-in orbit. In addition, all other known transiting planets have circular orbits.
The most likely explanation is the presence of a second, outer world whose gravity pulls on HAT-P-2b and perturbs its orbit. Although existing data cannot confirm a second planet, they cannot rule it out either.
HAT-P-2b orbits the star HD 147506. With visual magnitude 8.7, HD 147506 is the fourth brightest star known to harbor a transiting planet, making the star (but not the planet) visible in a small, 3-inch telescope.
HAT-P-2b was discovered using a network of small, automated telescopes known as HATNet, which was designed and built by Bakos. The HAT network consists of six telescopes, four at the Smithsonian Astrophysical Observatory's Whipple Observatory in Arizona and two at its Submillimeter Array facility in Hawaii.
As part of an international campaign, the Wise HAT telescope, located in the Negev desert (Israel) also took part in the discovery. The HAT telescopes conduct robotic observations every clear night, each covering an area of the sky 300 times the size of the full moon with every exposure. About 26,000 individual observations were made to detect the periodic dips of intensity due to the transit.
Major funding for HATnet was provided by NASA.
More information about HAT is available online at http://www.hatnet.hu
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