Kepler-644 b
Astrophysical Synthesis & Habitability Characterization
Kepler-644 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-644, located approximately 4298.9 light-years (1318.05 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0255% across the stellar disk), this world measures 3.15 Earth radii (0.28 Jupiter radii) and has a measured mass of 10.1 Earth masses. Combining its mass and radius yields a mean bulk density of 1.78 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 20 km/s.
In its orbital architecture around Kepler-644, Kepler-644 b completes one full revolution every 3.174 Earth days at a semi-major axis of 0.04641 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 159.1 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 1655 K (+1382°C / +2520°F) and receiving 2,381.77 S⊕ (~3,241,589 W/m²), Kepler-644 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-644 is classified as a stellar host with an effective photospheric temperature of 6,747 K, a radius of 1.81 R☉, a mass of 1.49 M☉, an estimated bolometric luminosity of 6.091 L☉. Stellar evolution modeling indicates an estimated stellar age of 1.62 Gyr and a metallicity of [Fe/H] = 0.08 dex (metal-rich relative to the Sun). From Earth, Kepler-644 shines at apparent V-band magnitude 14.031 (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-644 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,747 K |
| Stellar Radius | 1.8100 R☉ |
| Stellar Mass | 1.4900 M☉ |
| Bolometric Luminosity | 6.091 L☉ |
| Metallicity [Fe/H] | 0.080 dex |
| Stellar Age | 1.620 Gyr |
| Apparent Magnitude | V: 14.031 · G: 13.960 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046410 AU |
| Orbital Period | 3.174 days |
| Mean Orbital Velocity | 159.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 78.6500° |
| Mean Bulk Density | 1.78 g/cm³ (20 km/s vesc) |
| Insolation Flux | 2381.7700 S⊕ (~3,241,589 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 4298.900 LY (1318.050 pc) |