Kepler-191 d
Astrophysical Synthesis & Habitability Characterization
Kepler-191 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-191, located approximately 1938.9 light-years (594.46 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0683% across the stellar disk), this world measures 2.28 Earth radii and has a measured mass of 5.82 Earth masses. Combining its mass and radius yields a mean bulk density of 2.71 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.9 km/s.
In its orbital architecture around Kepler-191, Kepler-191 d completes one full revolution every 5.945 Earth days at a semi-major axis of 0.06104 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 111.7 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 857 K (+584°C / +1083°F) and receiving 99.60 S⊕ (~135,556 W/m²), Kepler-191 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-191 is classified as a stellar host with an effective photospheric temperature of 5,215 K, a radius of 0.8 R☉, a mass of 0.84 M☉, an estimated bolometric luminosity of 0.425 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.9 Gyr and a metallicity of [Fe/H] = -0.05 dex (near-solar heavy-element abundance). From Earth, Kepler-191 shines at apparent V-band magnitude 14.987 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-191 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-191 d sharing its stellar neighborhood alongside Kepler-191 b, Kepler-191 c.
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-191 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,215 K |
| Stellar Radius | 0.8000 R☉ |
| Stellar Mass | 0.8400 M☉ |
| Bolometric Luminosity | 0.425 L☉ |
| Metallicity [Fe/H] | -0.050 dex |
| Stellar Age | 4.900 Gyr |
| Apparent Magnitude | V: 14.987 · G: 14.776 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.061040 AU |
| Orbital Period | 5.945 days |
| Mean Orbital Velocity | 111.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 86.2400° |
| Mean Bulk Density | 2.71 g/cm³ (17.9 km/s vesc) |
| Insolation Flux | 99.6000 S⊕ (~135,556 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1938.900 LY (594.464 pc) |