tres-4b

tres-4b is an extrasolar planet, and one of the largest exoplanets ever found, after wasp-12b, wasp-17b, ct chamaeleontis b (though the latter may be a brown dwarf), gq lupi b and hd 100546 b. it was discovered in 2006, and announced in 2007, by the trans-atlantic exoplanet survey, using the transit method. it is approximately away orbiting the star gsc 02620-00648, in the constellation hercules.
orbit.
a 2008 study concluded that the gsc 06200-00648 system (among others) is a binary star system allowing even more accurate determination of stellar and planetary parameters.
tres-4 orbits its primary star every 3.543 days and eclipses it when viewed from earth. 
the study in 2012, utilizing a rossiter-mclaughlin effect, have determined the planetary orbit is probably aligned with the equatorial plane of the star, misalignment equal to 6.3°.
physical characteristics.
the planet is slightly less massive than jupiter (0.919 ± 0.073 ) but its diameter is 79.9% larger; it was considered the largest planet ever found at the time, giving it an average density of only about a third of a gram per cubic centimetre, approximately the same as saturn's moon methone. this made tres-4b both the largest-known planet and the planet with the lowest-known density at the time of its discovery.
tres-4b's orbital radius is 0.05091 au, giving it a predicted surface temperature of about 1,782 k. this by itself is not enough to explain the planet's low density, however. it is not currently known why tres-4b is so large. the probable causes are the proximity to a parent star that is three to four times more luminous than the sun as well as the internal heat within the planet.

