KOI-1257 b
Astrophysical Synthesis & Habitability Characterization
KOI-1257 b is a confirmed gas giant exoplanet orbiting the star KOI-1257, located approximately 2139.6 light-years (656 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.7313% across the stellar disk), this world measures 10.54 Earth radii (0.94 Jupiter radii) and has a measured mass of 460.83 Earth masses (1.45 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.17 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 4.15 g⊕ (40.7 m/s²), and an escape velocity of 74 km/s.
In its orbital architecture around KOI-1257, KOI-1257 b completes one full revolution every 86.648 Earth days at a semi-major axis of 0.382 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 48 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.772, swinging from 0.0871 AU at periapsis out to 0.6769 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 511 K (+238°C / +460°F) and receiving 7.28 S⊕ (~9,908 W/m²), KOI-1257 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star KOI-1257 is classified as a solar-type yellow star of spectral type G5 V with an effective photospheric temperature of 5,520 K, a radius of 1.13 R☉, a mass of 0.99 M☉, an estimated bolometric luminosity of 1.064 L☉. Stellar evolution modeling indicates an estimated stellar age of 9.3 Gyr and a metallicity of [Fe/H] = 0.27 dex (metal-rich relative to the Sun). From Earth, KOI-1257 shines at apparent V-band magnitude 14.818 (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 | KOI-1257 |
| Spectral Type | G5 V |
| Effective Temp (Teff) | 5,520 K |
| Stellar Radius | 1.1300 R☉ |
| Stellar Mass | 0.9900 M☉ |
| Bolometric Luminosity | 1.064 L☉ |
| Metallicity [Fe/H] | 0.270 dex |
| Stellar Age | 9.300 Gyr |
| Apparent Magnitude | V: 14.818 · G: 14.642 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.382000 AU |
| Orbital Period | 86.648 days |
| Mean Orbital Velocity | 48 km/s |
| Orbital Eccentricity (e) | 0.77200 |
| Orbital Inclination (i) | 89.6600° |
| Mean Bulk Density | 2.17 g/cm³ (74 km/s vesc) |
| Insolation Flux | 7.2800 S⊕ (~9,908 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2139.600 LY (656.000 pc) |