Gliese 581 b

Planet· orbits Gliese 581

Gliese 581 b - the most massive confirmed planet here (~20 Earth masses), a warm Neptune-like world on a 5.4-day orbit. Never imaged.

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Key facts

Mass

1.22 × 10²⁶ kg

20.5 M⊕

Year

5.37 Earth days

Distance from Gliese 581

5,968,955 km

Mass: 1.22 × 10²⁶ kg · 20.5 M⊕
Radius: Not measured; No transit — radius is a model estimate for a Neptune-like world; true size unknown.

Semi-major axis: 5,968,955 km; From the NASA Exoplanet Archive (radial-velocity orbit)
Eccentricity: 0.03; From the NASA Exoplanet Archive (radial-velocity orbit)
Inclination: 0.00 °; From the NASA Exoplanet Archive (radial-velocity orbit)
Orbital period: 5.4 days; From the NASA Exoplanet Archive (radial-velocity orbit)
Perihelion: 5,789,886 km; Computed from the orbital elements
Aphelion: 6,148,024 km; Computed from the orbital elements
Mean orbital velocity: 80.9 km/s; Computed from the orbital elements

Bulk composition: A warm Neptune-mass world (~20 Earth masses), likely with a thick gas envelope; never imaged.
Cloud appearance: Appearance based on ESO/M. Kornmesser'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 Visual mode; Realism shows a plain spectral colour.

Insolation: 7.79 S⊕ · 7.79× the sunlight Earth receives; Computed from Gliese 581's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
Equilibrium temperature: 464 K (191 °C); Computed model value — not measured.

Method: Radial-velocity detection (stellar wobble)
Name: Designated 'b' as the second planet found around its star, following the IAU convention of lettering planets in discovery order from 'b'.

The first planet found at Gliese 581, announced in 2005 - a Neptune-mass world close to the star.

No official imagery available — this object has never been visited and no officially-licensed depiction exists.