Kepler-304 d
Astrophysical Synthesis & Habitability Characterization
Kepler-304 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-304, located approximately 1417.7 light-years (434.68 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1347% across the stellar disk), this world measures 2.75 Earth radii and has a measured mass of 8 Earth masses. Combining its mass and radius yields a mean bulk density of 2.12 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 19.1 km/s.
In its orbital architecture around Kepler-304, Kepler-304 d completes one full revolution every 9.653 Earth days at a semi-major axis of 0.08 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 90.2 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 611 K (+338°C / +640°F) and receiving 33.16 S⊕ (~45,131 W/m²), Kepler-304 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-304 is classified as a stellar host with an effective photospheric temperature of 4,731 K, a radius of 0.687 R☉, a mass of 0.737 M☉, an estimated bolometric luminosity of 0.212 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.09 Gyr and a metallicity of [Fe/H] = 0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-304 shines at apparent V-band magnitude 15.065 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-304 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-304 d sharing its stellar neighborhood alongside Kepler-304 e, Kepler-304 b, Kepler-304 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-304 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,731 K |
| Stellar Radius | 0.6870 R☉ |
| Stellar Mass | 0.7370 M☉ |
| Bolometric Luminosity | 0.212 L☉ |
| Metallicity [Fe/H] | 0.030 dex |
| Stellar Age | 2.090 Gyr |
| Apparent Magnitude | V: 15.065 · G: 14.831 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.080000 AU |
| Orbital Period | 9.653 days |
| Mean Orbital Velocity | 90.2 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.6700° |
| Mean Bulk Density | 2.12 g/cm³ (19.1 km/s vesc) |
| Insolation Flux | 33.1600 S⊕ (~45,131 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1417.700 LY (434.684 pc) |