Kepler-28 c
Astrophysical Synthesis & Habitability Characterization
Kepler-28 c is a confirmed super-earth exoplanet orbiting the star Kepler-28, located approximately 1429.7 light-years (438.36 parsecs) from the Solar System. First announced in 2011 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0657% across the stellar disk), this world measures 1.857 Earth radii and has a measured mass of 2.06 Earth masses. Combining its mass and radius yields a mean bulk density of 1.77 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.6 g⊕ (5.88 m/s²), and an escape velocity of 11.8 km/s.
In its orbital architecture around Kepler-28, Kepler-28 c completes one full revolution every 8.99 Earth days at a semi-major axis of 0.07519 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 91 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.017 (ranging from 0.0739 AU at periapsis to 0.0765 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 509 K (+236°C / +457°F) and receiving 35.90 S⊕ (~48,857 W/m²), Kepler-28 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-28 is classified as a low-mass red dwarf of spectral type M0 V with an effective photospheric temperature of 4,499 K, a radius of 0.664 R☉, a mass of 0.684 M☉, an estimated bolometric luminosity of 0.162 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.91 Gyr and a metallicity of [Fe/H] = 0.145 dex (metal-rich relative to the Sun). From Earth, Kepler-28 shines at apparent V-band magnitude 15.13 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-28 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-28 c sharing its stellar neighborhood alongside Kepler-28 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-28 |
| Spectral Type | M0 V |
| Effective Temp (Teff) | 4,499 K |
| Stellar Radius | 0.6640 R☉ |
| Stellar Mass | 0.6840 M☉ |
| Bolometric Luminosity | 0.162 L☉ |
| Metallicity [Fe/H] | 0.145 dex |
| Stellar Age | 1.910 Gyr |
| Apparent Magnitude | V: 15.130 · G: 15.026 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.075190 AU |
| Orbital Period | 8.99 days |
| Mean Orbital Velocity | 91 km/s |
| Orbital Eccentricity (e) | 0.01700 |
| Orbital Inclination (i) | 89.9800° |
| Mean Bulk Density | 1.77 g/cm³ (11.8 km/s vesc) |
| Insolation Flux | 35.8980 S⊕ (~48,857 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1429.700 LY (438.359 pc) |