HD 209458b
| Exoplanet | List of exoplanets | |
|---|---|---|
 |
||
| Parent star | ||
| Star | HD 209458 | |
| Constellation | Pegasus | |
| Right ascension | (α) | 22h 03m 10.8s |
| Declination | (δ) | +18° 53′ 04″ |
| Apparent magnitude | (mV) | 7.65 |
| Distance | 154 ly (47.1 pc) |
|
| Spectral type | G0V | |
| Mass | (m) | 1.13+0.03 −0.02 M☉ |
| Radius | (r) | 1.14+0.06 −0.05 R☉ |
| Temperature | (T) | 6000 ± 50 K |
| Metallicity | [Fe/H] | 0.00 ± 0.02 |
| Age | 4 ± 2 Gyr | |
| Orbital elements | ||
| Semi-major axis | (a) | 0.045 AU (6.7 Gm) |
| Periastron | (q) | 0.044 AU (6.6 Gm) |
| Apastron | (Q) | 0.046 AU (6.8 Gm) |
| Eccentricity | (e) | 0.014±0.009 |
| Orbital period | (P) | 3.52474541 ± 0.00000025 d |
| (84.5938898 h) | ||
| Inclination | (i) | 86.1 ± 0.1° |
| Argument of periastron |
(ω) | 83° |
| Time of periastron | (T0) | 2,452,854.825415 ± 0.00000025 JD |
| Semi-amplitude | (K) | 84.26 ± 0.81 m/s |
| Physical characteristics | ||
| Mass | (m) | 0.71 MJ |
| Radius | (r) | 1.35 ± 0.05 RJ |
| Density | (ρ) | 370 kg m−3 |
| Surface gravity | (g) | 9.4 m/s² (0.96 g) |
| Temperature | (T) | 1,130 ± 150 |
| Discovery information | ||
| Discovery date | November 5, 1999 | |
| Discoverer(s) |
D. Charbonneau T. Brown D. Latham M. Mayor G.W. Henry G. Marcy Kerry O'Connor R.P. Butler S.S. Vogt |
|
| Discovery method | Radial velocity | |
| Other detection methods |
Transit (both primary and secondary), Reflection/emission modulations |
|
| Discovery site |
Lowell Observatory Geneva Observatory |
|
| Discovery status | Published | |
| Other designations | ||
|
Osiris
|
||
| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
| Exoplanet Archive | data | |
| Open Exoplanet Catalogue | data | |
HD 209458 b (sometimes unofficially called Osiris) is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some 150 light-years from the Solar System. The radius of the planet's orbit is 7 million kilometres, about 0.047 astronomical units, or one eighth the radius of Mercury's orbit. This small radius results in a year that is 3.5 Earth days long and an estimated surface temperature of about 1,000 °C (about 1,800 °F). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and volume of HD 209458 b indicate that it is a gas giant.
HD 209458 b represents a number of milestones in extraplanetary research. It was the first of many categories:
Based on the application of new, theoretical models, as of April 2007, it is alleged to be the first extrasolar planet found to have water vapor in its atmosphere.
In July, 2014, NASA announced finding very dry atmospheres on HD 209458 b and two other exoplanets (HD 189733 b and WASP-12b) orbiting Sun-like stars.
Spectroscopic studies first revealed the presence of a planet around HD 209458 on November 5, 1999. Astronomers had made careful photometric measurements of several stars known to be orbited by planets, in the hope that they might observe a dip in brightness caused by the transit of the planet across the star's face. This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected.
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