Kepler-357 d
Astrophysical Synthesis & Habitability Characterization
Kepler-357 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-357, located approximately 2245.8 light-years (688.57 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1422% across the stellar disk), this world measures 3.43 Earth radii (0.31 Jupiter radii) and has a measured mass of 11.6 Earth masses. Combining its mass and radius yields a mean bulk density of 1.59 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 20.6 km/s.
In its orbital architecture around Kepler-357, Kepler-357 d completes one full revolution every 49.5 Earth days at a semi-major axis of 0.246 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 54.1 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 402 K (+129°C / +264°F) and receiving 4.62 S⊕ (~6,286 W/m²), Kepler-357 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-357 is classified as a stellar host with an effective photospheric temperature of 5,036 K, a radius of 0.834 R☉, a mass of 0.794 M☉, an estimated bolometric luminosity of 0.401 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.14 Gyr and a metallicity of [Fe/H] = 0.06 dex (metal-rich relative to the Sun). From Earth, Kepler-357 shines at apparent V-band magnitude 15.735 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-357 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-357 d sharing its stellar neighborhood alongside Kepler-357 b, Kepler-357 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-357 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,036 K |
| Stellar Radius | 0.8340 R☉ |
| Stellar Mass | 0.7940 M☉ |
| Bolometric Luminosity | 0.401 L☉ |
| Metallicity [Fe/H] | 0.060 dex |
| Stellar Age | 2.140 Gyr |
| Apparent Magnitude | V: 15.735 · G: 15.522 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.246000 AU |
| Orbital Period | 49.5 days |
| Mean Orbital Velocity | 54.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.8600° |
| Mean Bulk Density | 1.59 g/cm³ (20.6 km/s vesc) |
| Insolation Flux | 4.6190 S⊕ (~6,286 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2245.800 LY (688.573 pc) |