Kepler-351 d
Astrophysical Synthesis & Habitability Characterization
Kepler-351 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-351, located approximately 3535.2 light-years (1083.91 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1022% across the stellar disk), this world measures 2.72 Earth radii and has a measured mass of 7.85 Earth masses. Combining its mass and radius yields a mean bulk density of 2.15 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.06 g⊕ (10.4 m/s²), and an escape velocity of 19 km/s.
In its orbital architecture around Kepler-351, Kepler-351 d completes one full revolution every 142.544 Earth days at a semi-major axis of 0.5177 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 39.5 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.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 2.720 R⊕, Kepler-351 d exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star Kepler-351 is classified as a stellar host with an effective photospheric temperature of 5,225 K, a radius of 0.78 R☉, a mass of 0.81 M☉, an estimated bolometric luminosity of 0.407 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.9 Gyr and a metallicity of [Fe/H] = -0.16 dex (metal-poor relative to the Sun). From Earth, Kepler-351 shines at apparent V-band magnitude 16.229 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-351 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-351 d sharing its stellar neighborhood alongside Kepler-351 b, Kepler-351 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-351 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,225 K |
| Stellar Radius | 0.7800 R☉ |
| Stellar Mass | 0.8100 M☉ |
| Bolometric Luminosity | 0.407 L☉ |
| Metallicity [Fe/H] | -0.160 dex |
| Stellar Age | 4.900 Gyr |
| Apparent Magnitude | V: 16.229 · G: 15.967 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.517700 AU |
| Orbital Period | 142.544 days |
| Mean Orbital Velocity | 39.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9900° |
| Mean Bulk Density | 2.15 g/cm³ (19 km/s vesc) |
| Insolation Flux | 1.9890 S⊕ (~2,707 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3535.200 LY (1083.910 pc) |