K2-18

Star

K2-18 — a cool red dwarf about a third of the Sun's mass, 124 light-years away in Leo. Faint and long-lived, it is the kind of star most planets orbit — and its habitable-zone sub-Neptune has made it one of the most-studied stars in the sky.

Open in 3D viewSee K2-18 in the live, interactive 3D map

Key facts

Mass

7.14 × 10²⁹ kg

0.359 M☉

Radius

285,933 km

41% of the Sun's radius

Surface temperature

3,457 K (3184 °C)

Luminosity

8.31 × 10²⁴ W

Spectral type

M2.5V (red dwarf)

Science

Physical

Mass: 7.14 × 10²⁹ kg · 0.359 M☉
Radius: 285,933 km · 41% of the Sun's radius
Density: 7,292 kg/m³ · 7.3× water
Spectral type: M2.5V (red dwarf)

Rotation

Note: A relatively quiet red dwarf, aiding the delicate atmospheric measurements of its planet.

Composition

By mass: A hydrogen/helium red dwarf about a third of the Sun's mass and ~2% of its light. Cool and long-lived, it is the commonest kind of star in the Galaxy — and its temperate sub-Neptune has made it one of the most-scrutinised.

Temperature

Surface: 3,457 K (3184 °C)

Radiation & temperature

Luminosity: 8.32 × 10²⁴ W · 0.0217 L☉
Surface temperature: 3,457 K (3184 °C)
Peak wavelength: 838 nm · near-infrared (mostly invisible to the eye)

Discovery & history

Name: A K2-mission catalogue designation; no proper name.

Catalogued by the K2 mission in 2015, when a planet was seen transiting it; the star has since been a prime JWST target because its planet sits in the temperate zone.

Images

Where to find it — in Leo, the Lion (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image