HD 80606 b

Planet· orbits the Sun

HD 80606 b — a giant of about 4 Jupiter masses on one of the most ECCENTRIC orbits known (e=0.93): it loops from ~0.85 AU in to just 0.03 AU from its star every 111 days. At closest approach it is flash-heated — models indicate its upper atmosphere can jump by ~500–700°C in hours — then cools on the long swing outward. Because it transits AND its mass is measured, its density is real. Never imaged.

Open in 3D viewSee HD 80606 b in the live, interactive 3D map

Key facts

Mass

7.90 × 10²⁷ kg

4.16 M♃ (1,324 M⊕)

Radius

73,712 km

11.6× wider than Earth

Surface gravity

97.1 m/s²

9.9× Earth's

Year

111 Earth days

Distance from HD 80606

0.46 AU

Science

Physical

Mass: 7.90 × 10²⁷ kg · 4.16 M♃ (1,324 M⊕)
Radius: 73,712 km · 11.6× wider than Earth
Density: 4,711 kg/m³ · 4.7× water
Surface gravity: 97.1 m/s² · 9.9× Earth's
Escape velocity: 120 km/s · 10.7× Earth's

Orbital

Semi-major axis: 0.46 AU
Eccentricity: 0.9318
Inclination: 0.00 °
Orbital period: 111.4 days
Perihelion: 4,696,245 km
Aphelion: 0.889 AU
Mean orbital velocity: 44.9 km/s

Composition

Bulk composition: A gas giant of ~4 Jupiter masses with a real measured density (transit + mass). Its defining trait is its orbit: an extreme ellipse (e=0.93) that carries it from ~0.85 AU in to just 0.03 AU from its star every 111 days. Near closest approach it is blasted with starlight and heats explosively — Spitzer watched it brighten as its atmosphere flash-heated — a natural experiment in planetary weather. Never imaged.
Cloud appearance: Appearance based on NASA/JPL-Caltech's artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The banded clouds shown are a representation of its class, shown only in Vision mode; Realism shows a plain spectral colour.

Radiation & temperature

Insolation: 4.5 S⊕ · 4.5× the sunlight Earth receives
Equilibrium temperature: 405 K (132 °C)

Discovery & history

Method: Transit detection
Name: Designated 'b' under the IAU convention that letters a star's planets 'b', 'c'… in the order found (the star is the unwritten 'a'); no IAU proper name is assigned.

Discovered by radial velocity in 2001; its transits (found 2009) confirmed the size, and Spitzer watched its atmosphere heat explosively during a periastron passage.

Images

Artist's concept of HD 80606 b being flash-heated at the close point of its wildly eccentric orbit (JWST) — an artist's impression, not a photograph. — NASA / ESA / CSA / J. Olmsted (STScI) (CC BY 4.0) · Wikimedia Commons

Images from open archives · credit shown per image