Kepler-20 g
Astrophysical Synthesis & Habitability Characterization
Kepler-20 g is a confirmed sub-neptune exoplanet orbiting the star Kepler-20, located approximately 921.6 light-years (282.56 parsecs) from the Solar System. First announced in 2016 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.71 Earth radii (0.42 Jupiter radii) and has a measured mass of 19.96 Earth masses. Combining its mass and radius yields a mean bulk density of 1.05 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.9 g⊕ (8.83 m/s²), and an escape velocity of 23 km/s.
In its orbital architecture around Kepler-20, Kepler-20 g completes one full revolution every 34.94 Earth days at a semi-major axis of 0.2055 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 64 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.15 carries the world between 0.1747 AU at periapsis and 0.2363 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 524 K (+251°C / +484°F) and receiving 16.21 S⊕ (~22,066 W/m²), Kepler-20 g orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-20 is classified as a stellar host with an effective photospheric temperature of 5,495 K, a radius of 0.9639 R☉, a mass of 0.948 M☉, an estimated bolometric luminosity of 0.76 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.6 Gyr and a metallicity of [Fe/H] = 0.07 dex (metal-rich relative to the Sun). From Earth, Kepler-20 shines at apparent V-band magnitude 12.61 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-20 system is a multi-planet architecture hosting 6 confirmed worlds, with Kepler-20 g sharing its stellar neighborhood alongside Kepler-20 b, Kepler-20 e, Kepler-20 c, Kepler-20 f, Kepler-20 d.
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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-20 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,495 K |
| Stellar Radius | 0.9639 R☉ |
| Stellar Mass | 0.9480 M☉ |
| Bolometric Luminosity | 0.76 L☉ |
| Metallicity [Fe/H] | 0.070 dex |
| Stellar Age | 7.600 Gyr |
| Apparent Magnitude | V: 12.610 · G: 12.454 |
| System Architecture | 2 Stars, 6 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.205500 AU |
| Orbital Period | 34.94 days |
| Mean Orbital Velocity | 64 km/s |
| Orbital Eccentricity (e) | 0.15000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.05 g/cm³ (23 km/s vesc) |
| Insolation Flux | 16.2132 S⊕ (~22,066 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 921.600 LY (282.563 pc) |