The hottest planet ever found is a sizzling 2250 °C – as hot as some stars. The find could challenge models of how close planets can sidle up to their host stars.
The new planet, known as WASP-12b, is 1.5 times as massive as Jupiter. Incredibly, it takes just over a day to circle its host star, orbiting at 1/40th the distance between the Earth and the Sun. The tight embrace heats WASP-12b to an estimated 2250 °Celsius – about half as hot as the surface of the Sun, and as hot as some stars.
That makes the planet the hottest yet discovered, as well as the planet with the fastest orbit, says Leslie Hebb of the University of St Andrews in the UK.
Hebb and colleagues found the giant in a large survey called the Super Wide Angle Search for Planets (SuperWASP). The collaboration uses two sets of telescopes, one in Spain's Canary Islands and the other in South Africa, to search for signs of 'transiting' planets, which pass in front of and dim their host stars as seen from Earth.
Extrasolar planets are too dim compared to their host stars to directly measure the infrared light – or heat – they emit. But astronomers know the planets' size and orbital distances from the transit observations. From that, they can work out how much starlight falls on the planets and thus take their temperature.
The competition for the hottest planet is tight. WASP-12b only just beats out the last record-holder, HD 149026b, whose blacker-than-charcoal surface is a searing 2040 °Celsius.
Puffy planetBut WASP-12b's speedy orbit might be a harder record to break. Astronomers believe Jupiter-sized exoplanets form farther from their stars and then migrate to closer orbits. That's because there could not have been enough gas and dust so close to the stars to amass such giant worlds.
Most observed exoplanets have orbital periods of three days or longer, Hebb says, suggesting that some mechanism may prevent the planets from migrating even closer to their stars.
"When the planets form and migrate inward, something is causing them to stop and preferentially stop with a period of three days," Hebb told New Scientist. "I was surprised that the period could be so much shorter."
WASP-12b's size may also be a challenge to explain. The planet's width is 1.8 times that of Jupiter, larger than gas giants are thought to grow.
"The planet radius is suspiciously large," notes Sara Seager of MIT. "While observation is leading theory, it's uncomfortable to have a planet with a radius that cannot be accommodated by theory."
So far the team does not have an explanation, but radiation from WASP-12b's host star could be puffing up the planet, Hebb says. The planet's composition, which might be rich in metals like its host star, may enhance the effect. Planets rich in heavy elements are expected to be less dense than their 'metal-poor' cousins.
The team next plans to look for ultraviolet light emanating from WASP-12b. Such observations could reveal whether the planet's atmosphere is being stripped or evaporated away by its host star.
http://space.newscientist.com/article/d ... found.html
The star is called HR 8799. It’s a bit more massive (1.5 times) and more luminous (5x) than the Sun, and lies about 130 light years from Earth. The planets in this picture orbit it at distances of 6 billion km (3.6 billion miles) and 10.5 billion km (6.3 billion miles). A third planet, not seen in this image but discovered later using the Keck 10 meter telescope, orbits the star closer in at a distance of 3.8 billion km (2.3 billion miles).
Newfound Planet Orbits Backward
Jeanna Bryner and Robert Roy Britt
SPACE.com Wed Aug 12, 11:21 am ET Updated 11:05 a.m. ET
Planets orbit stars in the same direction that the stars rotate. They all do. Except one.
A newfound planet orbits the wrong way, backward compared to the rotation of its host star. Its discoverers think a near-collision may have created the retrograde orbit, as it is called.
The star and its planet, WASP-17, are about 1,000 light-years away. The setup was found by the UK's Wide Area Search for Planets (WASP) project in collaboration with Geneva Observatory. The discovery was announced today but has not yet been published in a journal.
"I would have to say this is one of the strangest planets we know about," said Sara Seager, an astrophysicist at MIT who was not involved in the discovery.
What's going on
A star forms when a cloud of gas and dust collapses. Whatever movement the cloud had becomes intensified as it condenses, determining the rotational direction of the star. How planets form is less certain. They are, however, known to develop out of the leftover, typically disk-shaped mass of gas and dust that swirls around a newborn star, so whatever direction that material is moving, which is the direction of the star's rotation, becomes the direction of the planet's orbit.
WASP-17 likely had a close encounter with a larger planet, and the gravitational interaction acted like a slingshot to put WASP-17 on its odd course, the astronomers figure.
"I think it's extremely exciting. It's fascinating that we can study orbits of planets so far away," Seager told SPACE.com. "There's always theory, but there's nothing like an observation to really prove it."
Cosmic collisions are not uncommon. Earth's moon was made when our planet collided with a Mars-sized object, astronomers think. And earlier this week NASA's Spitzer Space Telescope found evidence of two planets colliding around a distant, young star. Some moons in our solar system are on retrograde orbits, perhaps at least in some cases because they were flying through space alone and then captured; that's thought to be the case with Neptune's large moon Triton.
The find was made by graduate students David Anderson at Keele University and Amaury Triaud of the Geneva Observatory.
WASP-17 is about half the mass of Jupiter but bloated to twice its size. "This planet is only as dense as expanded polystyrene, 70 times less dense than the planet we're standing on," said professor Coel Hellier of Keele University.
The bloated planet can be explained by a highly elliptical orbit, which brings it close to the star and then far away. Like exaggerated tides on Earth, the tidal effects on WASP-17 heat and stretch the planet, the researchers suggest.
The tides are not a daily affair, however. "Instead it's creating a huge amount of friction on the inside of the planet and generating a lot of energy, which might be making the planet big and puffy," Seager said.
WASP-17 is the 17th extrasolar planet found by the WASP project, which monitors hundreds of thousands of stars, watching for small dips in their light when a planet transits in front of them. NASA's Kepler space observatory is using the same technique to search for Earth-like worlds.
I agree with solrey, we cannot unequivocally assume that the planet is the offspring of the main star in that stellar system, it could have been captured or the system could have been otherwise disrupted at an earlier time. The article notes that the planet is on a highly ellipitical orbit,If planets are formed by fissioning off a star due to electric stress, then what are the parameters that constrain the new planets behavior? What conditions could produce the retrograde orbit of a newly fissioned body?
The bloated planet can be explained by a highly elliptical orbit, which brings it close to the star and then far away.
I wonder if this "bloated" form can in any way, be translated as a cometary? a tail perhaps?
nick c wrote:I agree with solrey, we cannot unequivocally assume that the planet is the offspring of the main star in that stellar system, it could have been captured or the system could have been otherwise disrupted at an earlier time. The article notes that the planet is on a highly ellipitical orbit,The bloated planet can be explained by a highly elliptical orbit, which brings it close to the star and then far away.
which is what one would expect from an interloper. I wonder if this "bloated" form can in any way, be translated as a cometary? a tail perhaps?
Or if the Planet's size fluctuates due to changing electrical stress at different points of this elliptical orbit.
Red stars are those stars that cannot satisfy their hunger for electrons from the surrounding plasma. So the star expands the surface area over which it collects electrons by growing a large plasma sheath that becomes the effective collecting area of the stellar anode in space. The growth process is self-limiting because, as the sheath expands, its electric field will grow stronger. Electrons caught up in the field are accelerated to ever-greater energies. Before long, they become energetic enough to excite neutral particles they chance to collide with, and the huge sheath takes on a uniform ‘red anode glow.’ It becomes a red giant star.
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