Kepler-1817 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1817 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1817, located approximately 2441.5 light-years (748.57 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0519% across the stellar disk), this world measures 2.273 Earth radii and has a measured mass of 5.79 Earth masses. Combining its mass and radius yields a mean bulk density of 2.72 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.12 g⊕ (10.98 m/s²), and an escape velocity of 17.9 km/s.
In its orbital architecture around Kepler-1817, Kepler-1817 b completes one full revolution every 44.299 Earth days at a semi-major axis of 0.2348 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 57.7 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 463 K (+190°C / +374°F) and receiving 10.85 S⊕ (~14,767 W/m²), Kepler-1817 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1817 is classified as a stellar host with an effective photospheric temperature of 5,316 K, a radius of 0.915 R☉, a mass of 0.878 M☉, an estimated bolometric luminosity of 0.6 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.4 Gyr and a metallicity of [Fe/H] = 0.16 dex (metal-rich relative to the Sun). From Earth, Kepler-1817 shines at apparent V-band magnitude 15.346 (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-1817 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,316 K |
| Stellar Radius | 0.9150 R☉ |
| Stellar Mass | 0.8780 M☉ |
| Bolometric Luminosity | 0.6 L☉ |
| Metallicity [Fe/H] | 0.160 dex |
| Stellar Age | 0.400 Gyr |
| Apparent Magnitude | V: 15.346 · G: 15.135 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.234800 AU |
| Orbital Period | 44.299 days |
| Mean Orbital Velocity | 57.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.4600° |
| Mean Bulk Density | 2.72 g/cm³ (17.9 km/s vesc) |
| Insolation Flux | 10.8500 S⊕ (~14,767 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2441.500 LY (748.569 pc) |