What is the biggest planet ever known?

Answer 1

According to the NASA Exoplanet Archive, the largest known exoplanet is DENIS-P J082303.1-491201 b. This planet is located 67.7 light years from Earth, and orbits a small brown dwarf. The planet is an enormous gas giant, with a mass of 28.5 +/- 1.9 Jupiter Masses.

Answer 2

TrES-4b is an extrasolar planet discovered in 2006 and announced in 2007 by the Trans-Atlantic Exoplanet Survey using the transit method. It is 1,400 light-years (430 pc) away in the constellation Hercules.[2]

TrES-4 orbits its primary star GSC 02620-00648 every 3.5 days and eclipses it when viewed from Earth. It is 0.919 times as massive as Jupiter but 1.799 times the diameter, the largest planet ever found (next to WASP-17b, and that was on 1 May 2009), giving it an average density of only about 0.333 grams per cubic centimetre. This made TrES-4 both the largest known planet and the planet with the lowest known density at the time of its discovery.[1][2]

Artist's conception of TrES-4 b.

TrES-4's orbital radius is 0.05091 AU, giving it a predicted surface temperature of about 1782 K. This by itself is not enough to explain the planet's low density, however. It is not currently known why TrES-4 is so large. The probable cause is the proximity to a parent star that is 3-4 times more luminous than the Sun and the internal heat within the planet.[1][2]

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.[1]. TrES-4b is also known as TrES 4 and is the biggest planet known to Man!

Answer 3

Jupiter is the largest known planet.