Kepler-1991 c
Astrophysical Synthesis & Habitability Characterization
Kepler-1991 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-1991, located approximately 2791.3 light-years (855.82 parsecs) from the Solar System. First announced in 2023 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0501% across the stellar disk), this world measures 2.57 Earth radii and has a measured mass of 7.13 Earth masses. Combining its mass and radius yields a mean bulk density of 2.32 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.08 g⊕ (10.59 m/s²), and an escape velocity of 18.6 km/s.
In its orbital architecture around Kepler-1991, Kepler-1991 c completes one full revolution every 22.79 Earth days at a semi-major axis of 0.1528 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 72.9 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 634 K (+361°C / +682°F) and receiving 38.27 S⊕ (~52,085 W/m²), Kepler-1991 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1991 is classified as a stellar host with an effective photospheric temperature of 5,478 K, a radius of 1.053 R☉, a mass of 0.914 M☉, an estimated bolometric luminosity of 0.896 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.76 Gyr and a metallicity of [Fe/H] = 0.16 dex (metal-rich relative to the Sun). From Earth, Kepler-1991 shines at apparent V-band magnitude 15.048 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-1991 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-1991 c sharing its stellar neighborhood alongside Kepler-1991 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-1991 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,478 K |
| Stellar Radius | 1.0530 R☉ |
| Stellar Mass | 0.9140 M☉ |
| Bolometric Luminosity | 0.896 L☉ |
| Metallicity [Fe/H] | 0.160 dex |
| Stellar Age | 6.760 Gyr |
| Apparent Magnitude | V: 15.048 · G: 14.721 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.152800 AU |
| Orbital Period | 22.79 days |
| Mean Orbital Velocity | 72.9 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9400° |
| Mean Bulk Density | 2.32 g/cm³ (18.6 km/s vesc) |
| Insolation Flux | 38.2700 S⊕ (~52,085 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2791.300 LY (855.820 pc) |