NASA (Exoplanet Catalog artwork)HD 209458 b
also named OsirisThe first planet seen crossing its star and the first with a detected atmosphere
Overview
HD 209458 b is an exoplanet, specifically a hot Jupiter, that orbits the solar analog HD 209458 in the constellation Pegasus, some 157 light-years from the Solar System. It is sometimes informally called Osiris. The radius of the planet's orbit is 0.047 AU, or one-eighth the radius of Mercury's orbit. This small orbital distance results in a year that is 3.5 Earth-days long and an estimated surface temperature of about 1,000 °C. Its mass is 220 times that of Earth 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.
Source: Wikipedia
NASA: HD 209458 b is a gas giant exoplanet that orbits a F-type star. Its mass is 0.73 Jupiters, it takes 3.5 days to complete one orbit of its star, and is 0.04707 AU from its star. Its discovery was announced in 1999.
Why it matters
- Its 1999 transit let astronomers measure an exoplanet's size and density for the first time.
- Sodium was detected in its atmosphere in 2001; later water, carbon monoxide and methane followed.
- Nicknamed Osiris because its hydrogen envelope is boiling off into a comet-like tail.
NASA puts it this way: “HD 209458 b is a gas giant exoplanet that orbits an F-type star. Its mass is 0.73 Jupiters, it takes 3.5 days to complete one orbit of its star, and is 0.04707 AU from its star. Its discovery was announced in 1999.”
Discovery & system
- Discovered
- 1999 · Radial Velocity · W. M. Keck Observatory
- Discovery paper
- Henry et al. 2000
- Discoverers
- Michel Mayor, David Charbonneau
- Host star
- HD 209458 · G0 V · 6,091 K · 1.23 M☉
- System
- 1 known planet
The system
| World | Period | Distance | Radius | Mass | Temp. |
|---|---|---|---|---|---|
| HD 209458 b | 3.52 d | 0.047 AU | 1.39 R♃ | 0.73 M♃ | 1,459 K |
By the numbers
- Radius
- 1.39 R♃15.6 R⊕
- Mass
- 0.73 M♃232 M⊕
- Orbital period
- 3.52 d0.01 yr
- Distance from star
- 0.047 AU7.04 million km
- Eccentricity
- 0nearly circular
- Equilibrium temp.
- 1,459 K1,186 °C
- Starlight received
- 587 × Earth
- Distance from Earth
- 158 ly48.3 pc
- Density
- 0.36 g/cm³0.07 × Earth
Sources
Image: NASA (Exoplanet Catalog artwork) · NASA media: generally free of copyright · image page
Text: Wikipedia (CC BY-SA 4.0). Taglines and highlights are editorial.