Kepler-398 c
Astrophysical Synthesis & Habitability Characterization
Kepler-398 c is a confirmed terrestrial exoplanet orbiting the star Kepler-398, located approximately 578.5 light-years (177.36 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0228% across the stellar disk), this world measures 1.01 Earth radii and has a measured mass of 1.01 Earth masses. Combining its mass and radius yields a mean bulk density of 5.41 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 11.2 km/s.
In its orbital architecture around Kepler-398, Kepler-398 c completes one full revolution every 11.419 Earth days at a semi-major axis of 0.087 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 82.9 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 536 K (+263°C / +505°F) and receiving 20.56 S⊕ (~27,977 W/m²), Kepler-398 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-398 is classified as a stellar host with an effective photospheric temperature of 4,493 K, a radius of 0.613 R☉, a mass of 0.649 M☉, an estimated bolometric luminosity of 0.137 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.34 Gyr and a metallicity of [Fe/H] = 0.053 dex (metal-rich relative to the Sun). From Earth, Kepler-398 shines at apparent V-band magnitude 13.499 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-398 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-398 c sharing its stellar neighborhood alongside Kepler-398 b, Kepler-398 d.
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-398 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,493 K |
| Stellar Radius | 0.6130 R☉ |
| Stellar Mass | 0.6490 M☉ |
| Bolometric Luminosity | 0.137 L☉ |
| Metallicity [Fe/H] | 0.053 dex |
| Stellar Age | 2.340 Gyr |
| Apparent Magnitude | V: 13.499 · G: 13.235 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.087000 AU |
| Orbital Period | 11.419 days |
| Mean Orbital Velocity | 82.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 85.3800° |
| Mean Bulk Density | 5.41 g/cm³ (11.2 km/s vesc) |
| Insolation Flux | 20.5560 S⊕ (~27,977 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 578.500 LY (177.355 pc) |