Kepler-25 d
Astrophysical Synthesis & Habitability Characterization
Kepler-25 d is a confirmed gas giant exoplanet orbiting the star Kepler-25, located approximately 793.4 light-years (243.25 parsecs) from the Solar System. First announced in 2014 by W. M. Keck Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 10 Earth radii (0.89 Jupiter radii) and has a measured mass of 71.9 Earth masses (0.23 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.4 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.72 g⊕ (7.06 m/s²), and an escape velocity of 30 km/s.
In its orbital architecture around Kepler-25, Kepler-25 d completes one full revolution every 122.4 Earth days at a semi-major axis of 0.416422 AU (situated at an orbital separation between Mercury's 0.39 AU and Venus's 0.72 AU). Its mean orbital velocity is approximately 37 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.13 carries the world between 0.3623 AU at periapsis and 0.4706 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 545 K (+272°C / +522°F) and receiving 15.22 S⊕ (~20,720 W/m²), Kepler-25 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-25 is classified as a warm F-type star of spectral type F8 with an effective photospheric temperature of 6,354 K, a radius of 1.316 R☉, a mass of 1.165 M☉, an estimated bolometric luminosity of 2.533 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.75 Gyr and a metallicity of [Fe/H] = 0.11 dex (metal-rich relative to the Sun). From Earth, Kepler-25 shines at apparent V-band magnitude 10.769 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-25 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-25 d sharing its stellar neighborhood alongside Kepler-25 b, Kepler-25 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-25 |
| Spectral Type | F8 |
| Effective Temp (Teff) | 6,354 K |
| Stellar Radius | 1.3160 R☉ |
| Stellar Mass | 1.1650 M☉ |
| Bolometric Luminosity | 2.533 L☉ |
| Metallicity [Fe/H] | 0.110 dex |
| Stellar Age | 2.750 Gyr |
| Apparent Magnitude | V: 10.769 · G: 10.632 |
| System Architecture | 2 Stars, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.416422 AU |
| Orbital Period | 122.4 days |
| Mean Orbital Velocity | 37 km/s |
| Orbital Eccentricity (e) | 0.13000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.4 g/cm³ (30 km/s vesc) |
| Insolation Flux | 15.2243 S⊕ (~20,720 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 793.400 LY (243.249 pc) |