Kepler-220 d
Astrophysical Synthesis & Habitability Characterization
Kepler-220 d is a confirmed terrestrial exoplanet orbiting the star Kepler-220, located approximately 558.1 light-years (171.11 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0182% across the stellar disk), this world measures 0.98 Earth radii and has a measured mass of 0.904 Earth masses. Combining its mass and radius yields a mean bulk density of 5.3 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 0.94 g⊕ (9.22 m/s²), and an escape velocity of 10.7 km/s.
In its orbital architecture around Kepler-220, Kepler-220 d completes one full revolution every 28.122 Earth days at a semi-major axis of 0.163 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 63.1 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 401 K (+128°C / +262°F) and receiving 8.21 S⊕ (~11,171 W/m²), Kepler-220 d orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-220 is classified as a stellar host with an effective photospheric temperature of 4,632 K, a radius of 0.666 R☉, a mass of 0.729 M☉, an estimated bolometric luminosity of 0.183 L☉. Stellar evolution modeling indicates an estimated stellar age of 6 Gyr and a metallicity of [Fe/H] = -0.174 dex (metal-poor relative to the Sun). From Earth, Kepler-220 shines at apparent V-band magnitude 13.049 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-220 system is a multi-planet architecture hosting 4 confirmed worlds, with Kepler-220 d sharing its stellar neighborhood alongside Kepler-220 b, Kepler-220 c, Kepler-220 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: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-220 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 4,632 K |
| Stellar Radius | 0.6660 R☉ |
| Stellar Mass | 0.7290 M☉ |
| Bolometric Luminosity | 0.183 L☉ |
| Metallicity [Fe/H] | -0.174 dex |
| Stellar Age | 6.000 Gyr |
| Apparent Magnitude | V: 13.049 · G: 12.857 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.163000 AU |
| Orbital Period | 28.122 days |
| Mean Orbital Velocity | 63.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.3400° |
| Mean Bulk Density | 5.3 g/cm³ (10.7 km/s vesc) |
| Insolation Flux | 8.2080 S⊕ (~11,171 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 558.100 LY (171.109 pc) |