K2-198 d
Astrophysical Synthesis & Habitability Characterization
K2-198 d is a confirmed sub-neptune exoplanet orbiting the star K2-198, located approximately 360.6 light-years (110.57 parsecs) from the Solar System. First announced in 2019 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0872% across the stellar disk), this world measures 2.438 Earth radii and has a measured mass of 6.52 Earth masses. Combining its mass and radius yields a mean bulk density of 2.48 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.1 g⊕ (10.79 m/s²), and an escape velocity of 18.3 km/s.
In its orbital architecture around K2-198, K2-198 d completes one full revolution every 7.45 Earth days.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 943 K (+670°C / +1238°F), K2-198 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star K2-198 is classified as a stellar host with an effective photospheric temperature of 5,213 K, a radius of 0.757 R☉, a mass of 0.799 M☉, an estimated bolometric luminosity of 0.38 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.094 dex (metal-rich relative to the Sun). From Earth, K2-198 shines at apparent V-band magnitude 10.971 (faint and requiring research-grade or CCD telescopic photometry) in the Southern celestial hemisphere. The K2-198 system is a multi-planet architecture hosting 3 confirmed worlds, with K2-198 d sharing its stellar neighborhood alongside K2-198 c, K2-198 b.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | K2-198 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,213 K |
| Stellar Radius | 0.7570 R☉ |
| Stellar Mass | 0.7990 M☉ |
| Bolometric Luminosity | 0.38 L☉ |
| Metallicity [Fe/H] | 0.094 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.971 · G: 10.996 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | — |
| Orbital Period | 7.45 days |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | 89.8600° |
| Mean Bulk Density | 2.48 g/cm³ (18.3 km/s vesc) |
| Insolation Flux | — |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 360.600 LY (110.567 pc) |