Kepler-198 b
Astrophysical Synthesis & Habitability Characterization
Kepler-198 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-198, located approximately 1615.6 light-years (495.36 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0756% across the stellar disk), this world measures 2.82 Earth radii and has a measured mass of 8.35 Earth masses. Combining its mass and radius yields a mean bulk density of 2.05 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 19.2 km/s.
In its orbital architecture around Kepler-198, Kepler-198 b completes one full revolution every 17.79 Earth days at a semi-major axis of 0.131 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 80.1 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 655 K (+382°C / +720°F) and receiving 44.55 S⊕ (~60,631 W/m²), Kepler-198 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-198 is classified as a stellar host with an effective photospheric temperature of 5,574 K, a radius of 0.94 R☉, a mass of 0.995 M☉, an estimated bolometric luminosity of 0.765 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.51 Gyr and a metallicity of [Fe/H] = 0.114 dex (metal-rich relative to the Sun). From Earth, Kepler-198 shines at apparent V-band magnitude 13.684 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-198 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-198 b sharing its stellar neighborhood alongside Kepler-198 d, Kepler-198 c.
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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-198 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,574 K |
| Stellar Radius | 0.9400 R☉ |
| Stellar Mass | 0.9950 M☉ |
| Bolometric Luminosity | 0.765 L☉ |
| Metallicity [Fe/H] | 0.114 dex |
| Stellar Age | 0.510 Gyr |
| Apparent Magnitude | V: 13.684 · G: 13.566 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.131000 AU |
| Orbital Period | 17.79 days |
| Mean Orbital Velocity | 80.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.6600° |
| Mean Bulk Density | 2.05 g/cm³ (19.2 km/s vesc) |
| Insolation Flux | 44.5490 S⊕ (~60,631 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1615.600 LY (495.358 pc) |