XO-2Nb (or rarely XO-2Bb) is an extrasolar planet orbiting the star XO-2N, the fainter component of XO-2 wide binary star in the constellation Lynx.^[2] This planet was found by the transit method in 2007 by Burke et al. This was the second such planet found by the XO telescope.

XO-2Nb (XO-2Bb)

Size comparison of XO-2 b (gray) with Jupiter.
Discovery
Discovered by	Burke et al.
Discovery date	2007
Detection method	Transit (including secondary eclipse)
Orbital characteristics
Semi-major axis	0.0369 ± 0.002 AU (5,520,000 ± 300,000 km)
Eccentricity	0
Orbital period (sidereal)	2.61586178 ± 0.00000075[1] d
Inclination	87.62 ± 0.51[1]
Time of periastron	2454147.74902 ± 0.00002
Argument of periastron	?
Semi-amplitude	80.2
Star	XO-2N (XO-2B)
Physical characteristics
Mean radius	0.973 ± 0.03 RJ
Mass	0.57 ± 0.06 MJ
Mean density	820 kg/m3 (1,380 lb/cu yd)
Surface gravity	1.42 m/s2 (4.7 ft/s2)
Temperature	1208

Like most planets found by the transit method, it is a roughly Jupiter sized planet that orbits very close to its host star; in this case, it has a surface temperature of about 1200 K, so it belongs to a group of exoplanets known as hot Jupiters. The planet takes 2.6 days to orbit the star at the average distance of 0.0369 AU. The planet has mass of 57% of Jupiter and radius of 97% of Jupiter. The radius is relatively large for its mass, probably due to its intense heating from its nearby star that bloats the planet's atmosphere. The large radius for its mass gives a low density of 820 kg/m³.^[3]