Kepler-817 b
Astrophysical Synthesis & Habitability Characterization
Kepler-817 b is a confirmed gas giant exoplanet orbiting the star Kepler-817, located approximately 4841.7 light-years (1484.46 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.646% across the stellar disk), this world measures 9.03 Earth radii (0.81 Jupiter radii) and has a measured mass of 60.2 Earth masses (0.19 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.45 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.74 g⊕ (7.26 m/s²), and an escape velocity of 28.9 km/s.
In its orbital architecture around Kepler-817, Kepler-817 b completes one full revolution every 3.99 Earth days at a semi-major axis of 0.0493 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 134.4 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 1124 K (+851°C / +1564°F) and receiving 550.20 S⊕ (~748,826 W/m²), Kepler-817 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-817 is classified as a stellar host with an effective photospheric temperature of 5,861 K, a radius of 1.03 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.123 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.55 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-817 shines at apparent V-band magnitude 15.967 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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-817 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,861 K |
| Stellar Radius | 1.0300 R☉ |
| Stellar Mass | 1.0300 M☉ |
| Bolometric Luminosity | 1.123 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | 3.550 Gyr |
| Apparent Magnitude | V: 15.967 · G: 15.597 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.049300 AU |
| Orbital Period | 3.99 days |
| Mean Orbital Velocity | 134.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 87.0900° |
| Mean Bulk Density | 0.45 g/cm³ (28.9 km/s vesc) |
| Insolation Flux | 550.2030 S⊕ (~748,826 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4841.700 LY (1484.460 pc) |