XO-3b is an

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

with about 11.79 times the mass of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...

, and it orbits its parent

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

in about 3.2 days.Oddball Planet Puzzles Astronomers, ''Space.com''
/ref> The radius of this object is 1.217 times that of Jupiter. Astronomers announced their discovery on May 30, 2007, at the American Astronomical Society in

Honolulu, Hawaii Honolulu (; ) is the capital and largest city of the U.S. state of Hawaii, which is in the Pacific Ocean. It is an unincorporated county seat of the consolidated City and County of Honolulu, situated along the southeast coast of the islan ...

. Its discovery is attributed to the combined effort of amateur and professional astronomers working together on the

XO Project The XO Project is an international team of amateur and professional astronomers tasked with identifying extrasolar planets. They are led by Peter R. McCullough of the Space Telescope Science Institute. It is primarily funded by NASA's Origins Progr ...

using a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

located on the Haleakala summit in Hawaii. Dubbed an "oddball" planet, at the time of its discovery the planet was the most massive planet found in close proximity to a star, yet the orbit is significantly elliptical instead of circular, as would be expected. It is also considered a

transiting planet In astronomy, a transit (or astronomical transit) is a phenomenon when a celestial body passes directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of th ...

, passing in front of its parent star during each orbit. It is the third such planet to be found by the XO Project which was specifically created to locate them.

Planetary orbit

Measurements of the

Rossiter–McLaughlin effect The Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when an object moves across the face of a star. Description The Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when either an eclipsing binary's second ...

allow a determination of the angle between the planet's orbital plane and the equator of the parent star. Initial reports suggested this angle was very large, at 70 ± 15 degrees, which is significantly larger than that of the other transiting planets for which this measurement has been made. The authors cautioned that

systematic Systematic may refer to: Science * Short for systematic error * Systematic fault * Systematic bias, errors that are not determined by chance but are introduced by an inaccuracy (involving either the observation or measurement process) inheren ...

effects may have affected the measurements, and a later determination by an independent group of astronomers determined a reduced value of 37.3°. This value is, however, still larger than the misalignment between the Sun's equator and the orbital plane of Jupiter, which is only 6°. 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 In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values b ...

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 In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relations ...

with XO-3b. Another planetary system that may have also undergone such planet–planet interactions is Upsilon Andromedae. Due to tidal dissipation, the planetary orbital period is decaying at a rate of , 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.

Atmosphere

Observations of several transits in the near ultraviolet by the

Neil Gehrels Swift Observatory Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a NASA three-telescope space observatory for studying gamma-ray bursts (GRBs) and monitoring the afterglow in X-ray, and UV/Visible light at the locatio ...

results in a measured planetary radius, in the near ultraviolet, of 2.54 times that of

Debate

There is currently a debate over the classification of this object as either a

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a ...

or a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen (hydrogen-1, 1H) into helium in their cores, unlike a main sequence, main-sequence star. Instead, they have ...

. 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. The light curve that best matches the steepness of ingress and egress implies a planetary radius of and a mass of .

References

External links

Kjempeplanet i farta
- forskning.no 1.6.07 {{DEFAULTSORT:Xo-3b Camelopardalis Hot Jupiters Transiting exoplanets Giant planets Exoplanets discovered in 2007

Planetary orbit

Atmosphere

Debate

See also

References

External links