Kepler-51 d
Astrophysical Synthesis & Habitability Characterization
Kepler-51 d is a confirmed gas giant exoplanet orbiting the star Kepler-51, located approximately 2556.5 light-years (783.83 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.895% across the stellar disk), this world measures 9.7 Earth radii (0.87 Jupiter radii) and has a measured mass of 7.6 Earth masses. Combining its mass and radius yields a mean bulk density of 0.05 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.08 g⊕ (0.78 m/s²), and an escape velocity of 9.9 km/s.
In its orbital architecture around Kepler-51, Kepler-51 d completes one full revolution every 130.194 Earth days at a semi-major axis of 0.509 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 42.5 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.008 (ranging from 0.5049 AU at periapsis to 0.5131 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 381 K (+108°C / +226°F) and receiving 2.47 S⊕ (~3,356 W/m²), Kepler-51 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-51 is classified as a stellar host with an effective photospheric temperature of 6,018 K, a radius of 0.94 R☉, a mass of 1.04 M☉, an estimated bolometric luminosity of 1.04 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.3 Gyr and a metallicity of [Fe/H] = 0.05 dex (near-solar heavy-element abundance). From Earth, Kepler-51 shines at apparent V-band magnitude 14.885 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-51 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-51 d sharing its stellar neighborhood alongside Kepler-51 b, Kepler-51 c, Kepler-51 e.
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-51 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,018 K |
| Stellar Radius | 0.9400 R☉ |
| Stellar Mass | 1.0400 M☉ |
| Bolometric Luminosity | 1.04 L☉ |
| Metallicity [Fe/H] | 0.050 dex |
| Stellar Age | 0.300 Gyr |
| Apparent Magnitude | V: 14.885 · G: 14.678 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.509000 AU |
| Orbital Period | 130.194 days |
| Mean Orbital Velocity | 42.5 km/s |
| Orbital Eccentricity (e) | 0.00800 |
| Orbital Inclination (i) | 89.9100° |
| Mean Bulk Density | 0.05 g/cm³ (9.9 km/s vesc) |
| Insolation Flux | 2.4660 S⊕ (~3,356 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2556.500 LY (783.831 pc) |