Epsilon Eridani b

Planet· orbits Epsilon Eridani

Epsilon Eridani b (AEgir) — a gas giant of roughly Jupiter's mass orbiting the young Sun-like star Epsilon Eridani, 10.5 light-years away. It circles at about 3.5 AU on a near-circular 7.3-year orbit, outside the region where the debris disk's dust has been cleared. Its mass is genuinely measured (by astrometry), but it has never been imaged and never transits, so its size, appearance and composition are model-based.

Open in 3D viewSee Epsilon Eridani b in the live, interactive 3D map

Key facts

Mass

1.90 × 10²⁷ kg

1 M♃ (318 M⊕)

Year

7.35 Earth years

2,686 Earth days

Distance from Epsilon Eridani

3.53 AU

Science

Physical

Mass: 1.90 × 10²⁷ kg · 1 M♃ (318 M⊕)
Radius: Not measured; The mass is genuinely MEASURED (radial velocity + Gaia/HST astrometry, ~1 Jupiter), but the planet has never transited, so its radius is a model estimate for a gas giant of this mass (~1.2 Jupiter radii). Because density needs a measured radius, none is quoted here.

Orbital

Semi-major axis: 3.53 AU; From the NASA Exoplanet Archive (radial velocity + Gaia/HST astrometry)
Eccentricity: 0.06; From the NASA Exoplanet Archive (radial velocity + Gaia/HST astrometry)
Inclination: 0.00 °; From the NASA Exoplanet Archive (radial velocity + Gaia/HST astrometry)
Orbital period: 7.35 years; From the NASA Exoplanet Archive (radial velocity + Gaia/HST astrometry)
Perihelion: 3.32 AU; Computed from the orbital elements
Aphelion: 3.74 AU; Computed from the orbital elements
Mean orbital velocity: 14.3 km/s; Computed from the orbital elements

Composition

Bulk composition: A cold gas giant — hydrogen and helium with a deep atmosphere, roughly Jupiter's mass. It has never been imaged, so its true appearance is unknown; the map shows an honest flat spectral colour, not a fabricated cloud pattern.
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.

Radiation & temperature

Insolation: 0.0273 S⊕ · 3% of the sunlight Earth receives; Computed from Epsilon Eridani's luminosity and the orbital distance (inverse-square; Earth's sunlight = 1).
Equilibrium temperature: 112 K (-161 °C); Computed model value for its cold 3.5-AU orbit around a faint star — not measured.

Discovery & history

Discovered: August 1, 2000
By: Artie P. Hatzes et al.
Method: Radial-velocity detection (stellar wobble)
Name: Named AEgir — the Norse sea god, husband of Ran (the star) — in the IAU's 2015 NameExoWorlds campaign. Designated 'b' as the first planet found around Epsilon Eridani.

Announced in 2000 by Artie Hatzes and colleagues from radial-velocity data — one of the first giant planets found around a Sun-like star, though the signal was long debated because the young star is magnetically active and mimics planetary wobbles. Combined Hubble and Gaia astrometry (2023) finally confirmed it and pinned down its true mass (~1 Jupiter) and near-circular orbit.

Images

Artist's concept of Epsilon Eridani b (AEgir), the system's gas giant (foreground), amid the star's dusty belts — not a photograph; its true appearance is unknown — NASA / JPL-Caltech (public domain) · Wikimedia Commons

Images from open archives · credit shown per image