Kepler-68 d
Astrophysical Synthesis & Habitability Characterization
Kepler-68 d is a confirmed gas giant exoplanet orbiting the star Kepler-68, located approximately 470.2 light-years (144.17 parsecs) from the Solar System. First announced in 2013 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 13.9 Earth radii (1.24 Jupiter radii) and has a measured mass of 267 Earth masses (0.84 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.55 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.38 g⊕ (13.53 m/s²), and an escape velocity of 49 km/s.
In its orbital architecture around Kepler-68, Kepler-68 d completes one full revolution every 632.62 Earth days (1.73Julian years) at a semi-major axis of 1.469 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 25.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.102 carries the world between 1.3192 AU at periapsis and 1.6188 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.900 R⊕, Kepler-68 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-68 is classified as a stellar host with an effective photospheric temperature of 5,847 K, a radius of 1.2564 R☉, a mass of 1.057 M☉, an estimated bolometric luminosity of 1.655 L☉. Stellar evolution modeling indicates an estimated stellar age of 6.84 Gyr and a metallicity of [Fe/H] = 0.11 dex (metal-rich relative to the Sun). From Earth, Kepler-68 shines at apparent V-band magnitude 10.077 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-68 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-68 d sharing its stellar neighborhood alongside Kepler-68 b, Kepler-68 c, Kepler-68 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-68 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,847 K |
| Stellar Radius | 1.2564 R☉ |
| Stellar Mass | 1.0570 M☉ |
| Bolometric Luminosity | 1.655 L☉ |
| Metallicity [Fe/H] | 0.110 dex |
| Stellar Age | 6.840 Gyr |
| Apparent Magnitude | V: 10.077 · G: 9.934 |
| System Architecture | 2 Stars, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.469000 AU |
| Orbital Period | 632.62 days |
| Mean Orbital Velocity | 25.3 km/s |
| Orbital Eccentricity (e) | 0.10200 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.55 g/cm³ (49 km/s vesc) |
| Insolation Flux | 0.7889 S⊕ (~1,074 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 470.200 LY (144.166 pc) |