Kepler-217 d
Astrophysical Synthesis & Habitability Characterization
Kepler-217 d is a confirmed super-earth exoplanet orbiting the star Kepler-217, located approximately 3602.8 light-years (1104.64 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0047% across the stellar disk), this world measures 1.32 Earth radii and has a measured mass of 2.3 Earth masses. Combining its mass and radius yields a mean bulk density of 5.51 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.32 g⊕ (12.94 m/s²), and an escape velocity of 14.8 km/s.
In its orbital architecture around Kepler-217, Kepler-217 d completes one full revolution every 3.887 Earth days at a semi-major axis of 0.0534 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 149.5 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 1574 K (+1301°C / +2374°F) and receiving 2,099.75 S⊕ (~2,857,762 W/m²), Kepler-217 d 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 6,341 K, a radius of 1.76 R☉, a mass of 1.37 M☉, an estimated bolometric luminosity of 4.493 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.63 Gyr and a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). 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 d sharing its stellar neighborhood alongside Kepler-217 b, 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) | 6,341 K |
| Stellar Radius | 1.7600 R☉ |
| Stellar Mass | 1.3700 M☉ |
| Bolometric Luminosity | 4.493 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | 2.630 Gyr |
| Apparent Magnitude | V: 13.155 · G: 13.121 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.053400 AU |
| Orbital Period | 3.887 days |
| Mean Orbital Velocity | 149.5 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7500° |
| Mean Bulk Density | 5.51 g/cm³ (14.8 km/s vesc) |
| Insolation Flux | 2099.7520 S⊕ (~2,857,762 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3602.800 LY (1104.640 pc) |