Kepler-217 b
Astrophysical Synthesis & Habitability Characterization
Kepler-217 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-217, located approximately 3602.8 light-years (1104.64 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0129% across the stellar disk), this world measures 2.23 Earth radii and has a measured mass of 5.6 Earth masses. Combining its mass and radius yields a mean bulk density of 2.78 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.7 km/s.
In its orbital architecture around Kepler-217, Kepler-217 b completes one full revolution every 5.375 Earth days at a semi-major axis of 0.065 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 131.6 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 1413 K (+1140°C / +2084°F) and receiving 1,366.48 S⊕ (~1,859,775 W/m²), Kepler-217 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-217 is classified as a stellar host with an effective photospheric temperature of 6,171 K, a radius of 1.799 R☉, a mass of 1.342 M☉, an estimated bolometric luminosity of 4.211 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.4 Gyr and a metallicity of [Fe/H] = -0.07 dex (near-solar heavy-element abundance). From Earth, Kepler-217 shines at apparent V-band magnitude 13.155 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-217 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-217 b sharing its stellar neighborhood alongside Kepler-217 d, Kepler-217 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-217 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,171 K |
| Stellar Radius | 1.7990 R☉ |
| Stellar Mass | 1.3420 M☉ |
| Bolometric Luminosity | 4.211 L☉ |
| Metallicity [Fe/H] | -0.070 dex |
| Stellar Age | 2.400 Gyr |
| Apparent Magnitude | V: 13.155 · G: 13.121 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.065000 AU |
| Orbital Period | 5.375 days |
| Mean Orbital Velocity | 131.6 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 88.7300° |
| Mean Bulk Density | 2.78 g/cm³ (17.7 km/s vesc) |
| Insolation Flux | 1366.4770 S⊕ (~1,859,775 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3602.800 LY (1104.640 pc) |