HAT-P-9b

HAT-P-9b, formally named Alef,^[1] is an exoplanet approximately 1500 light years away in the constellation Auriga. This planet was found by the transit method on June 26, 2008. It has a mass 78% that of Jupiter and a radius 140% that of Jupiter. As with most transiting planets, this planet is a hot Jupiter, meaning this Jupiter-like planet orbits extremely close to its parent star, taking only 3.92 days to orbit.^[2]

HAT-P-9b / Alef

Size comparison of HAT-P-9b with Jupiter.
Discovery
Discovered by	Shporer et al.
Discovery site	Cambridge, Massachusetts
Discovery date	June 26, 2008
Detection method	Transit (SuperWASP)
Orbital characteristics
Semi-major axis	0.0528 ± 0.002 AU (7,900,000 ± 300,000 km)
Eccentricity	~0.0012
Orbital period (sidereal)	3.92289 ± 0.00004 d
Star	HAT-P-9
Physical characteristics
Mean radius	1.4 ± 0.06 RJ
Mass	0.78 ± 0.09 MJ
Mean density	0.38 g/cm3
Surface gravity	10.3 m/s2 (34 ft/s2) 1.05 g

The study in 2012, utilizing a Rossiter–McLaughlin effect, have determined the planetary orbit is mildly misaligned with the rotational axis of the star, misalignment equal to -16±8°.^[3]

The name Alef was selected in the NameExoWorlds campaign by Israel, during the 100th anniversary of the IAU. Alef is the first letter in the Hebrew alphabet and also means bull.^[1]