Team finds largest exoplanet yet [ TrES-4 ]

The "transiting" planet - meaning one that passes in front of its parent star as seen from Earth - is about 70% larger than Jupiter. But the presumed "gas giant" has a much lower mass than Jupiter - the biggest planet in our Solar System - making it of extremely low density... The new exoplanet, called TrES-4, is located in the constellation of Hercules and was discovered by a team working on the Transatlantic Exoplanet Survey (TrES)... TrES-4 circles the star GSC02620-00648, which lies about 1,435 light-years away from Earth. Being only about seven million km (4.5 million miles) from its parent star, the planet is also very hot, about 1,327C (1,600 K; 2,300F). Because of the relatively weak pull exerted by TrES-4 on its upper atmosphere, some of the atmosphere probably escapes in a curved comet-like tail. "TrES-4 is the largest known exoplanet," said lead author Georgi Mandushev, from the Lowell Observatory in Flagstaff, US. It is so big, in fact, that its size is difficult to explain using current theories about superheated giant planets... Its density of 0.2 grams per cubic centimetre is so low that the planet would, in theory, float on water... "TrES-4 blocks off about 1% of the light of the star as it passes in front of it," said Dr Mandushev... Planet TrES-4 makes a complete revolution around its parent star every 3.55 days, so a year on this planet is shorter than a week on Earth.

Searching the Next 2000 Stars for Hot Jupiters
N2K Project Overview
Ongoing precise radial velocity surveys of ~2000 stars have discovered over 150 extrasolar planets, including many "Hot Jupiters": massive planets orbiting surprisingly close to their host stars. Fortuitous alignment of the orbital planes has caused three such planets to transit in front of bright host stars, revealing a wealth of information about these planets: density, composition, and even interior structure... Using the now well-established correlation between host stars' heavy element abundance and the frequency of planets, we select high metallicity stars from a pool of 14,000, and distribute them to three observatories: Keck, Subaru and Magellan. Precise radial velocities obtained over three nights at these observatories identify candidate hot jupiters for intense monitoring. Planets then found in small orbits (P < 14 days) have relatively high probability for transit (~10%) and are monitored photometrically at Fairborn Observatory. A full description of our technique can be found in the first paper below.

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