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SARG-TNG contributes to the follow-up observations of the hottest extrasolar planet yet discovered

An international team of astronomers reports the discovery of a planet that sizzles at about 2500 degrees Celsius, which is as hot as some stars.

The new planet, known as WASP-12b, is about 1.4 times as massive as Jupiter. It takes just over a day to circle its host star (2MASS J063032.79+294020.4 , hereafter WASP-12), orbiting at only 1/40th the distance between the Earth and the Sun.

The values of the temperature and of the orbital period make of this planet the hottest yet discovered, as well as the planet with the fastest orbit.

WASP-12b was found in the context of a large survey called the Super Wide Angle Search for Planets (SuperWASP). The survey is performed by using two sets of telescopes, one in Spain (Canary Islands) and the other in South Africa, to search for signs of 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.

High resolution spectroscopy with SARG-TNG played an important role in the follow-up observations and characterization of the WASP-12 - WASP-12b system.

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, suggesting that some mechanism may prevent the planets from migrating even closer to their stars. Therefore, it was surprising that WASP-12b could orbit with a so short period.

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.

(L. Hebb et al., "WASP-12b: The Hottest Transiting Extrasolar Planet Yet Discovered", 2009, Astrophysical Journal, vol. 693, pages 1920-1928)

Figure 1. An artists' impression of WASP-12b. (Credit: NASA/Fredrick Pont).