TrES-4b

TrES-4b is an exoplanet. It was discovered in 2006, and announced in 2007, by the Trans-Atlantic Exoplanet Survey, using the transit method. At the time of its discovery TrES-4 was the largest confirmed exoplanet ever found, now more than 10 larger planets have been discovered. It is approximately 1,400 light-years (430 pc) away orbiting the star GSC 02620-00648, in the constellation Hercules.^[1]

TrES-4b

Size comparison of TrES-4 with Jupiter
Discovery
Discovered by	Mandushev et al[1]
Discovery date	2006–2007
Detection method	Transit
Orbital characteristics
Semi-major axis	0.05091 ± 0.00071 AU (7.616 ± 0.106 million km)[2]
Eccentricity	0
Orbital period (sidereal)	3.553945 ± 0.000075 d
Inclination	82.86 ± 0.33[2]
Semi-amplitude	86.1
Star	GSC 02620-00648 A[2]
Physical characteristics
Mean radius	1.838+0.240 −0.238 RJ[3]
Mass	0.78±0.19 MJ[3]
Mean density	0.156+0.072 −0.071 g/cm3[3]
Surface gravity	7.04 ± 1.12 m/s2 (23.1 ± 3.7 ft/s2) 0.718 ± 0.114 g
Temperature	1,782±29 K (1,509 °C; 2,748 °F, equilibrium)[2]

Orbit

TrES-4 orbits its primary star every 3.543 days and eclipses it when viewed from Earth.

A 2008 study concluded that the GSC 02620-00648 system (among others) is a binary star system allowing even more accurate determination of stellar and planetary parameters.^[2]

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±4.7°.^[4]

Physical characteristics

The planet is slightly less massive than Jupiter (0.919 ± 0.073 M_J) but its diameter is 84% larger. This give TrES-4 an average density of only about a third of a gram per cubic centimetre, approximately the same as Saturn's moon Methone. At the time of its discovery in 2007, TrES-4 was both the largest-known planet and the planet with the lowest-known density.^[2][1]

TrES-4b's orbital radius is 0.05091 AU, giving it a predicted surface temperature of about 1,782 K (1,509 °C; 2,748 °F). 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.^[2][1]

See also

• List of exoplanet extremes
• WASP-17b, another large exoplanet