Kepler-557 b
Astrophysical Synthesis & Habitability Characterization
Kepler-557 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-557, located approximately 6839.9 light-years (2097.12 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0445% across the stellar disk), this world measures 2.67 Earth radii and has a measured mass of 7.61 Earth masses. Combining its mass and radius yields a mean bulk density of 2.2 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.07 g⊕ (10.49 m/s²), and an escape velocity of 18.9 km/s.
In its orbital architecture around Kepler-557, Kepler-557 b completes one full revolution every 3.706 Earth days at a semi-major axis of 0.0469 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 137.7 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 1281 K (+1008°C / +1846°F) and receiving 2,885.66 S⊕ (~3,927,387 W/m²), Kepler-557 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-557 is classified as a stellar host with an effective photospheric temperature of 6,068 K, a radius of 1.16 R☉, a mass of 1.11 M☉, an estimated bolometric luminosity of 1.637 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.24 Gyr and a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, Kepler-557 shines at apparent V-band magnitude 14.723 (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-557 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,068 K |
| Stellar Radius | 1.1600 R☉ |
| Stellar Mass | 1.1100 M☉ |
| Bolometric Luminosity | 1.637 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | 3.240 Gyr |
| Apparent Magnitude | V: 14.723 · G: 14.639 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.046900 AU |
| Orbital Period | 3.706 days |
| Mean Orbital Velocity | 137.7 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 82.0500° |
| Mean Bulk Density | 2.2 g/cm³ (18.9 km/s vesc) |
| Insolation Flux | 2885.6630 S⊕ (~3,927,387 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 6839.900 LY (2097.120 pc) |