Kepler-104 d
Astrophysical Synthesis & Habitability Characterization
Kepler-104 d is a confirmed sub-neptune exoplanet orbiting the star Kepler-104, located approximately 1307.2 light-years (400.79 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0592% across the stellar disk), this world measures 3.58 Earth radii (0.32 Jupiter radii) and has a measured mass of 5.54 Earth masses. Combining its mass and radius yields a mean bulk density of 0.67 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.43 g⊕ (4.22 m/s²), and an escape velocity of 13.9 km/s.
In its orbital architecture around Kepler-104, Kepler-104 d completes one full revolution every 51.755 Earth days at a semi-major axis of 0.257 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 54 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 515 K (+242°C / +468°F) and receiving 16.01 S⊕ (~21,792 W/m²), Kepler-104 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-104 is classified as a stellar host with an effective photospheric temperature of 5,711 K, a radius of 1.349 R☉, a mass of 0.818 M☉, an estimated bolometric luminosity of 1.737 L☉. Stellar evolution modeling indicates an estimated stellar age of 13.18 Gyr and a metallicity of [Fe/H] = -0.42 dex (metal-poor relative to the Sun). From Earth, Kepler-104 shines at apparent V-band magnitude 12.697 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-104 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-104 d sharing its stellar neighborhood alongside Kepler-104 b, Kepler-104 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-104 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,711 K |
| Stellar Radius | 1.3490 R☉ |
| Stellar Mass | 0.8180 M☉ |
| Bolometric Luminosity | 1.737 L☉ |
| Metallicity [Fe/H] | -0.420 dex |
| Stellar Age | 13.180 Gyr |
| Apparent Magnitude | V: 12.697 · G: 12.570 |
| System Architecture | 2 Stars, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.257000 AU |
| Orbital Period | 51.755 days |
| Mean Orbital Velocity | 54 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.1400° |
| Mean Bulk Density | 0.67 g/cm³ (13.9 km/s vesc) |
| Insolation Flux | 16.0120 S⊕ (~21,792 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 1307.200 LY (400.785 pc) |