XO-3b

The misalignment may indicate that in the past an encounter with another planet altered its orbit, kicking it out of the plane of the planetary system. Its orbital eccentricity is very large (e = 0.2883). Since tidal forces should have reduced the orbital eccentricity of this planet it is possible that there is another massive planet outside the orbit of XO-3 that is in orbital resonance with XO-3b.^[12] Another planetary system that may have also undergone such planet–planet interactions is Upsilon Andromedae.^[13]

Due to tidal dissipation, the planetary orbital period is decaying at a rate of (6.2±0.29)×10⁻⁹, or about 1.7 ms per orbit. At this rate, the planet will be engulfed by its star in about 1.4 million years. However, unlike the similar planet WASP-12b, it is unlikely to be experiencing significant mass loss.^[14][15]

Atmosphere

Observations of several transits in the near ultraviolet by the Neil Gehrels Swift Observatory results in a measured planetary radius, in the near ultraviolet, of 2.54 times that of Jupiter.^[16]

Debate

There is currently a debate over the classification of this object as either a planet or a brown dwarf. One of the leading astronomers in this discussion is Christopher Johns-Krull, who indicated that the debate is still quite lively. This is not particularly unusual or strange, as it would not be the first of many brown dwarfs orbiting mother stars.^[7]

The light curve that best matches the steepness of ingress and egress implies a planetary radius of 1.32 ± 0.15 R_J and a mass of 11.71 ± 0.46 M_J.^[1]

See also

• XO Telescope

References