Kepler-1921 c
Astrophysical Synthesis & Habitability Characterization
Kepler-1921 c is a confirmed super-earth exoplanet orbiting the star Kepler-1921, located approximately 3030 light-years (928.99 parsecs) from the Solar System. First announced in 2023 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0042% across the stellar disk), this world measures 1.41 Earth radii and has a measured mass of 2.57 Earth masses. Combining its mass and radius yields a mean bulk density of 5.06 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.29 g⊕ (12.65 m/s²), and an escape velocity of 15.1 km/s.
In its orbital architecture around Kepler-1921, Kepler-1921 c completes one full revolution every 3.157 Earth days at a semi-major axis of 0.0454 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 156.4 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 1791 K (+1518°C / +2764°F) and receiving 2,436.47 S⊕ (~3,316,036 W/m²), Kepler-1921 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1921 is classified as a stellar host with an effective photospheric temperature of 6,120 K, a radius of 2 R☉, a mass of 1.251 M☉, an estimated bolometric luminosity of 5.034 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.39 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-1921 shines at apparent V-band magnitude 13.103 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-1921 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-1921 c sharing its stellar neighborhood alongside Kepler-1921 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-1921 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,120 K |
| Stellar Radius | 2.0000 R☉ |
| Stellar Mass | 1.2510 M☉ |
| Bolometric Luminosity | 5.034 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | 3.390 Gyr |
| Apparent Magnitude | V: 13.103 · G: 12.984 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.045400 AU |
| Orbital Period | 3.157 days |
| Mean Orbital Velocity | 156.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9900° |
| Mean Bulk Density | 5.06 g/cm³ (15.1 km/s vesc) |
| Insolation Flux | 2436.4700 S⊕ (~3,316,036 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3030.000 LY (928.989 pc) |