Kepler-42 c
Astrophysical Synthesis & Habitability Characterization
Kepler-42 c is a confirmed sub-earth exoplanet orbiting the star Kepler-42, located approximately 130.7 light-years (40.06 parsecs) from the Solar System. First announced in 2011 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.155% across the stellar disk), this world measures 0.73 Earth radii and has a measured mass of 60.337 Earth masses (0.19 Jupiter masses). Combining its mass and radius yields a mean bulk density of 855.23 g/cm³ (an iron-enriched, high-compression rocky core), a surface gravity of 113.22 g⊕ (1110.31 m/s²), and an escape velocity of 101.7 km/s.
In its orbital architecture around Kepler-42, Kepler-42 c completes one full revolution every 0.453 Earth days at a semi-major axis of 0.006 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 144 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 720 K (+447°C / +837°F) and receiving 82.13 S⊕ (~111,772 W/m²), Kepler-42 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-42 is classified as a low-mass red dwarf of spectral type M with an effective photospheric temperature of 3,068 K, a radius of 0.17 R☉, a mass of 0.13 M☉, an estimated bolometric luminosity of 0.00230 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.5 Gyr and a metallicity of [Fe/H] = -0.33 dex (metal-poor relative to the Sun). From Earth, Kepler-42 shines at apparent V-band magnitude 16.7 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-42 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-42 c sharing its stellar neighborhood alongside Kepler-42 b, Kepler-42 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-42 |
| Spectral Type | M |
| Effective Temp (Teff) | 3,068 K |
| Stellar Radius | 0.1700 R☉ |
| Stellar Mass | 0.1300 M☉ |
| Bolometric Luminosity | 0.00230 L☉ |
| Metallicity [Fe/H] | -0.330 dex |
| Stellar Age | 4.500 Gyr |
| Apparent Magnitude | V: 16.700 · G: 14.993 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.006000 AU |
| Orbital Period | 0.453 days |
| Mean Orbital Velocity | 144 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 81.1100° |
| Mean Bulk Density | 855.23 g/cm³ (101.7 km/s vesc) |
| Insolation Flux | 82.1250 S⊕ (~111,772 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 130.700 LY (40.060 pc) |