TrES-4

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**TrES-4**
Parent star
Extrasolar planet		List of extrasolar planets
Star		GSC 02620-00648^[1]
Constellation		Hercules
Right ascension	(α)	17^h 53^m 13^s
Declination	(δ)	+37° 12′ 42″
Distance		1400 ± 200 ly (430 ± 60 pc)
Spectral type		F
Orbital elements
Semimajor axis	(a)	0.0488 AU
Eccentricity	(e)	0
Orbital period	(P)	3.553945 d
Inclination	(i)	82.81°
Angular distance	(θ)	0.111 mas
Semi-amplitude	(K)	86.1 m/s
Physical characteristics
Mass	(m)	0.84 M_J
Radius	(r)	1.674 R_J
Density	(ρ)	240 kg/m³
Surface gravity	(g)	6.93 m/s² (0.71 g)
Temperature	(T)	1,600 K
Discovery information
Discovery date		2006^[2]
Discoverer(s)		Mandushev et al.
Detection method		Transit
Discovery status		Published

TrES-4 is an exoplanet discovered in 2006^[2] by the Trans-Atlantic Exoplanet Survey using the transit method. It is 1400 light years away in the constellation Hercules.^[3]

TrES-4 orbits its primary star every 3.5 days and eclipses it when viewed from Earth. It is 0.84 times as massive as Jupiter but 1.674 times the diameter, the largest planet ever found, giving it an average density of only about 0.24 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, a so-called "fluffy" or "puffy planet".^[3]

TrES-4's orbital radius is 7.3 million kilometres, giving it a predicted surface temperature of about 1300 ºC. 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 parent star 3-4 times as luminous than the Sun and internal heat within the planet.^[3]

TrES-4's primary star is 1.22 times as massive as the Sun. It has run out of hydrogen fuel in its core and has begun to grow into a red giant star; in less than a billion years it is expected to merge and engulf TrES-4.^[3]