Kepler-198 d
Astrophysical Synthesis & Habitability Characterization
Kepler-198 d is a confirmed super-earth exoplanet orbiting the star Kepler-198, located approximately 1615.6 light-years (495.36 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0227% across the stellar disk), this world measures 1.53 Earth radii and has a measured mass of 2.96 Earth masses. Combining its mass and radius yields a mean bulk density of 4.56 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.26 g⊕ (12.36 m/s²), and an escape velocity of 15.6 km/s.
In its orbital architecture around Kepler-198, Kepler-198 d completes one full revolution every 1.312 Earth days at a semi-major axis of 0.02342 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 194.2 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 1562 K (+1289°C / +2352°F) and receiving 1,444.52 S⊕ (~1,965,986 W/m²), Kepler-198 d 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 5,636 K, a radius of 0.93 R☉, a mass of 0.97 M☉, an estimated bolometric luminosity of 0.783 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.72 Gyr and a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). 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 d sharing its stellar neighborhood alongside Kepler-198 b, 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) | 5,636 K |
| Stellar Radius | 0.9300 R☉ |
| Stellar Mass | 0.9700 M☉ |
| Bolometric Luminosity | 0.783 L☉ |
| Metallicity [Fe/H] | 0.040 dex |
| Stellar Age | 3.720 Gyr |
| Apparent Magnitude | V: 13.684 · G: 13.566 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.023420 AU |
| Orbital Period | 1.312 days |
| Mean Orbital Velocity | 194.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.7800° |
| Mean Bulk Density | 4.56 g/cm³ (15.6 km/s vesc) |
| Insolation Flux | 1444.5160 S⊕ (~1,965,986 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1615.600 LY (495.358 pc) |