Kepler-390 c
Astrophysical Synthesis & Habitability Characterization
Kepler-390 c is a confirmed sub-earth exoplanet orbiting the star Kepler-390, located approximately 1419.7 light-years (435.28 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0087% across the stellar disk), this world measures 0.79 Earth radii and has a measured mass of 0.418 Earth masses. Combining its mass and radius yields a mean bulk density of 4.67 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.67 g⊕ (6.57 m/s²), and an escape velocity of 8.1 km/s.
In its orbital architecture around Kepler-390, Kepler-390 c completes one full revolution every 13.06 Earth days at a semi-major axis of 0.101 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 84.1 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 630 K (+357°C / +675°F) and receiving 41.35 S⊕ (~56,279 W/m²), Kepler-390 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-390 is classified as a stellar host with an effective photospheric temperature of 5,166 K, a radius of 0.776 R☉, a mass of 0.787 M☉, an estimated bolometric luminosity of 0.385 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.24 Gyr and a metallicity of [Fe/H] = -0.044 dex (near-solar heavy-element abundance). From Earth, Kepler-390 shines at apparent V-band magnitude 14.231 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-390 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-390 c sharing its stellar neighborhood alongside Kepler-390 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-390 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,166 K |
| Stellar Radius | 0.7760 R☉ |
| Stellar Mass | 0.7870 M☉ |
| Bolometric Luminosity | 0.385 L☉ |
| Metallicity [Fe/H] | -0.044 dex |
| Stellar Age | 3.240 Gyr |
| Apparent Magnitude | V: 14.231 · G: 13.922 |
| System Architecture | 2 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.101000 AU |
| Orbital Period | 13.06 days |
| Mean Orbital Velocity | 84.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.0800° |
| Mean Bulk Density | 4.67 g/cm³ (8.1 km/s vesc) |
| Insolation Flux | 41.3510 S⊕ (~56,279 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1419.700 LY (435.277 pc) |