Kepler-656 b
Astrophysical Synthesis & Habitability Characterization
Kepler-656 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-656, located approximately 2903.9 light-years (890.35 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1217% across the stellar disk), this world measures 3.12 Earth radii (0.28 Jupiter radii) and has a measured mass of 9.91 Earth masses. Combining its mass and radius yields a mean bulk density of 1.8 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 19.9 km/s.
In its orbital architecture around Kepler-656, Kepler-656 b completes one full revolution every 1.26 Earth days at a semi-major axis of 0.02231 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 192.6 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 1569 K (+1296°C / +2365°F) and receiving 924.37 S⊕ (~1,258,073 W/m²), Kepler-656 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-656 is classified as a stellar host with an effective photospheric temperature of 5,281 K, a radius of 0.82 R☉, a mass of 0.86 M☉, an estimated bolometric luminosity of 0.469 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.37 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, Kepler-656 shines at apparent V-band magnitude 15.549 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-656 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-656 b sharing its stellar neighborhood alongside Kepler-656 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-656 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,281 K |
| Stellar Radius | 0.8200 R☉ |
| Stellar Mass | 0.8600 M☉ |
| Bolometric Luminosity | 0.469 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 4.370 Gyr |
| Apparent Magnitude | V: 15.549 · G: 15.337 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.022310 AU |
| Orbital Period | 1.26 days |
| Mean Orbital Velocity | 192.6 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 77.1700° |
| Mean Bulk Density | 1.8 g/cm³ (19.9 km/s vesc) |
| Insolation Flux | 924.3740 S⊕ (~1,258,073 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2903.900 LY (890.352 pc) |