Kepler-278 c
Astrophysical Synthesis & Habitability Characterization
Kepler-278 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-278, located approximately 1445 light-years (443.03 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.011% across the stellar disk), this world measures 3.268 Earth radii (0.29 Jupiter radii) and has a measured mass of 34.9 Earth masses (0.11 Jupiter masses). Combining its mass and radius yields a mean bulk density of 5.51 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 3.27 g⊕ (32.07 m/s²), and an escape velocity of 36.6 km/s.
In its orbital architecture around Kepler-278, Kepler-278 c completes one full revolution every 51.111 Earth days at a semi-major axis of 0.287 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 61.1 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.616, swinging from 0.1102 AU at periapsis out to 0.4638 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 492 K (+219°C / +426°F) and receiving 54.30 S⊕ (~73,902 W/m²), Kepler-278 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-278 is classified as an orange K-type star of spectral type K2 III-IV with an effective photospheric temperature of 4,965 K, a radius of 2.861 R☉, a mass of 1.227 M☉, an estimated bolometric luminosity of 4.463 L☉. Stellar evolution modeling indicates an estimated stellar age of 5.761 Gyr and a metallicity of [Fe/H] = 0.22 dex (metal-rich relative to the Sun). From Earth, Kepler-278 shines at apparent V-band magnitude 11.811 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-278 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-278 c sharing its stellar neighborhood alongside Kepler-278 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-278 |
| Spectral Type | K2 III-IV |
| Effective Temp (Teff) | 4,965 K |
| Stellar Radius | 2.8610 R☉ |
| Stellar Mass | 1.2270 M☉ |
| Bolometric Luminosity | 4.463 L☉ |
| Metallicity [Fe/H] | 0.220 dex |
| Stellar Age | 5.761 Gyr |
| Apparent Magnitude | V: 11.811 · G: 11.530 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.287000 AU |
| Orbital Period | 51.111 days |
| Mean Orbital Velocity | 61.1 km/s |
| Orbital Eccentricity (e) | 0.61600 |
| Orbital Inclination (i) | 88.5800° |
| Mean Bulk Density | 5.51 g/cm³ (36.6 km/s vesc) |
| Insolation Flux | 54.3000 S⊕ (~73,902 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1445.000 LY (443.030 pc) |