Kepler-1321 c
Astrophysical Synthesis & Habitability Characterization
Kepler-1321 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-1321, located approximately 2508.6 light-years (769.15 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1724% across the stellar disk), this world measures 2.4 Earth radii and has a measured mass of 6.35 Earth masses. Combining its mass and radius yields a mean bulk density of 2.53 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.1 g⊕ (10.79 m/s²), and an escape velocity of 18.2 km/s.
In its orbital architecture around Kepler-1321, Kepler-1321 c completes one full revolution every 2.226 Earth days at a semi-major axis of 0.0267 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 130.5 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 697 K (+424°C / +795°F) and receiving 115.91 S⊕ (~157,752 W/m²), Kepler-1321 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1321 is classified as a stellar host with an effective photospheric temperature of 4,094 K, a radius of 0.53 R☉, a mass of 0.54 M☉, an estimated bolometric luminosity of 0.071 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.17 Gyr and a metallicity of [Fe/H] = -0.45 dex (metal-poor relative to the Sun). From Earth, Kepler-1321 shines at apparent V-band magnitude 17.505 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-1321 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-1321 c sharing its stellar neighborhood alongside Kepler-1321 d, Kepler-1321 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-1321 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,094 K |
| Stellar Radius | 0.5300 R☉ |
| Stellar Mass | 0.5400 M☉ |
| Bolometric Luminosity | 0.071 L☉ |
| Metallicity [Fe/H] | -0.450 dex |
| Stellar Age | 4.170 Gyr |
| Apparent Magnitude | V: 17.505 · G: 16.928 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.026700 AU |
| Orbital Period | 2.226 days |
| Mean Orbital Velocity | 130.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7300° |
| Mean Bulk Density | 2.53 g/cm³ (18.2 km/s vesc) |
| Insolation Flux | 115.9090 S⊕ (~157,752 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2508.600 LY (769.146 pc) |