Kepler-1128 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1128 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1128, located approximately 3533.6 light-years (1083.41 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1352% across the stellar disk), this world measures 3.65 Earth radii (0.33 Jupiter radii) and has a measured mass of 12.9 Earth masses. Combining its mass and radius yields a mean bulk density of 1.46 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.97 g⊕ (9.51 m/s²), and an escape velocity of 21 km/s.
In its orbital architecture around Kepler-1128, Kepler-1128 b completes one full revolution every 61.618 Earth days at a semi-major axis of 0.302 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 53.3 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 424 K (+151°C / +304°F) and receiving 6.45 S⊕ (~8,780 W/m²), Kepler-1128 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1128 is classified as a stellar host with an effective photospheric temperature of 5,543 K, a radius of 0.91 R☉, a mass of 0.94 M☉, an estimated bolometric luminosity of 0.701 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.57 Gyr and a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). From Earth, Kepler-1128 shines at apparent V-band magnitude 15.934 (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-1128 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,543 K |
| Stellar Radius | 0.9100 R☉ |
| Stellar Mass | 0.9400 M☉ |
| Bolometric Luminosity | 0.701 L☉ |
| Metallicity [Fe/H] | 0.040 dex |
| Stellar Age | 4.570 Gyr |
| Apparent Magnitude | V: 15.934 · G: 15.686 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.302000 AU |
| Orbital Period | 61.618 days |
| Mean Orbital Velocity | 53.3 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.9600° |
| Mean Bulk Density | 1.46 g/cm³ (21 km/s vesc) |
| Insolation Flux | 6.4510 S⊕ (~8,780 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 3533.600 LY (1083.410 pc) |