Well, wish upon a star!: astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts have announced that they have found the most massive known transiting extrasolar planet. The gas giant planet, called HAT-P-2b, contains more than eight times the mass of Jupiter, the biggest planet in our solar system. Its powerful gravity squashes it into a ball only slightly larger than Jupiter.
"Planet X" is as heavy as 25,000 Earths, has temperatures higher than 2000 degrees Fahrenheit, gravity 15 times stronger than Earth's, and a year that lasts just 5.6 days, according to The intense gravity means a person who weighs 150 pounds on Earth would weigh more than 2,000 pounds on HAT.
"HAT" has an extremely oval orbit that brings it as close as 3.1 million miles from its star before swinging three times farther out, to a distance of 9.6 million miles. If Earth's orbit were as elliptical, we would loop from almost reaching Mercury out to almost reaching Mars. Because of its orbit, the planet gets enormously heated up when it passes close to the star, then cools off as it loops out again.
"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 Center for Astrophysics astronomer Gaspar Bakos. "But we eliminated every other possibility, so we knew we had a really weird planet."
The mega-planet orbits an F-type star, which is almost twice as big and somewhat hotter than the Sun, located about 440 light-years away in the constellation Hercules. Once every 5 days and 15 hours, it crosses directly in front of the star as viewed from Earth-a sort of mini-eclipse. Such a transit offers astronomers a unique opportunity to measure a planet's physical size from the amount of dimming.
By measuring how the star wobbles as the planet's gravity tugs it, astronomers deduced that 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, on the gas giant.
"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 the mega-planet is its highly eccentric 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 was discovered using a network of small, automated telescopes known as HATNet, which 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 Israel's Negev desert lso 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.
Posted by Casey Kazan.
Thursday, August 14, 2008
"Planet X" -Super-massive Planet Discovered
Astronomers have long speculated about the existence of a "Planet X" -a planet out there that's a real whopper, perhaps as much as ten times the size of Jupiter, a planet more like a sun that never quite made it, trillions of miles from our Solar System.