Epsilon Eridani
Epsilon Eridani (Ran) — a young orange dwarf (K2V) just 10.5 light-years away in Eridanus, the River, and one of the closest planetary systems to the Sun. Only ~200–850 million years old, it is still ringed by a dusty debris disk — a Kuiper-belt analogue — and hosts a confirmed gas giant. It is a snapshot of what the young Solar System may have looked like.
Key facts
Science
Physical
- Mass
- 1.63 × 10³⁰ kg · 0.82 M☉
- Radius
- 513,427 km · 74% of the Sun's radius
- Density
- 2,877 kg/m³ · 2.9× water
- Computed from mass and radius
- Spectral type
- K2V (orange dwarf)
Motion through space
- Proper motion
- 0.975 arcseconds per year · its drift across our sky
- SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
- Radial velocity
- +16.4 km/s · moving away from the Sun
- SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
- Speed across our line of sight
- 14.9 km/s
- Computed from proper motion and parallax
- Speed through space, relative to the Sun
- 22.1 km/s
- Computed from proper motion, parallax and radial velocity
Rotation
- Note
- Rotates rapidly for a K dwarf — about once every 11 days — a hallmark of its youth.
Composition
- By mass
- A hydrogen/helium orange dwarf a little smaller and cooler than the Sun. It is YOUNG (~200–850 Myr) and magnetically active, with strong starspots and chromospheric activity — that youthful activity long made its planet's radial-velocity signal hard to pin down.
Temperature
- Surface
- 5,084 K (4,811 °C)
Radiation & temperature
- Luminosity
- 1.30 × 10²⁶ W · 0.34 L☉
- Surface temperature
- 5,084 K (4,811 °C)
- Peak wavelength
- 570 nm · green-yellow visible light
- Computed (Wien's law) from the surface temperature
Discovery & history
- Method
- Naked-eye star
- Name
- Its IAU proper name Ran (approved 2015) is the Norse sea goddess who caught drowning sailors in her net; its planet is named AEgir, her husband. 'Epsilon Eridani' is the Bayer designation for a star in Eridanus, the celestial River.
Known since antiquity as a star of Eridanus, Epsilon Eridani was — like Tau Ceti — one of the two stars Frank Drake listened to in the 1960 Project Ozma search for alien radio signals. In 1998 sub-millimetre observations revealed a dusty debris ring around it, and in 2000 radial-velocity data revealed a giant planet — one of the first found around a Sun-like star. Its youth and nearness make it one of the most-studied planetary systems beyond our own.
Images
Images from open archives · credit shown per image