The star
The star
K2-198
- Type
- orange dwarf
- Surface
- ≈ 5,213 K
- Size
- 0.76 × the Sun
- Mass
- 0.80 × the Sun
- Brightness
- 0.397 × the Sun
- Habitable zone
- 0.488–1.17 AU
The planets
K2-198
K2-198 c
- Year
- 3.36 days
- Distance from star
- 0.0407 AU
- Mass
- 2.6 Earths
- Size
- 1.4 × Earth
- Temperature
- ≈ 1230 K (+957 °C)
- Found
- 2019, transit (K2)
K2-198
K2-198 d
- Year
- 7.45 days
- Distance from star
- 0.0693 AU
- Mass
- 6.5 Earths
- Size
- 2.4 × Earth
- Temperature
- ≈ 943 K (+670 °C)
- Found
- 2019, transit (K2)
K2-198
K2-198 b
- Year
- 17.04 days
- Distance from star
- 0.12 AU
- Mass
- 16 Earths
- Size
- 4.2 × Earth
- Temperature
- ≈ 716 K (+443 °C)
- Found
- 2018, transit (K2)
Masses found by the wobble method are minimums, because the orbit's tilt is unknown. Temperatures are equilibrium estimates for a bare planet, before any atmosphere.
How we know
The shadow
The planet passes in front of its star and dims it by a fraction of a percent, every orbit. The dip gives the planet's size and year.
Sources
- Planet and star parameters: NASA Exoplanet Archive, Planetary Systems Composite Parameters, retrieved 1 Nov 2026. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.
- Position: HYG Database v4.1 (CC BY-SA 4.0).
- Habitable zone: a simple estimate from the star's brightness (√L × 0.95 to 1.67 AU), shown as a guide.