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. See also
 List of exoplanet extremes
 WASP-17b, another large exoplanet

References

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Hercules (constellation)
Hot Jupiters
Transiting exoplanets
Exoplanets discovered in 2006
Giant planets