Kepler-728 b
Astrophysical Synthesis & Habitability Characterization
Kepler-728 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-728, located approximately 5757.4 light-years (1765.23 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1084% across the stellar disk), this world measures 3.34 Earth radii (0.3 Jupiter radii) and has a measured mass of 11.1 Earth masses. Combining its mass and radius yields a mean bulk density of 1.64 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1 g⊕ (9.81 m/s²), and an escape velocity of 20.4 km/s.
In its orbital architecture around Kepler-728, Kepler-728 b completes one full revolution every 5.743 Earth days at a semi-major axis of 0.0625 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 118.4 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 982 K (+709°C / +1308°F) and receiving 484.51 S⊕ (~659,418 W/m²), Kepler-728 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-728 is classified as a stellar host with an effective photospheric temperature of 5,660 K, a radius of 0.93 R☉, a mass of 0.95 M☉, an estimated bolometric luminosity of 0.796 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.07 Gyr and a metallicity of [Fe/H] = -0.03 dex (near-solar heavy-element abundance). From Earth, Kepler-728 shines at apparent V-band magnitude 15.585 (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-728 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,660 K |
| Stellar Radius | 0.9300 R☉ |
| Stellar Mass | 0.9500 M☉ |
| Bolometric Luminosity | 0.796 L☉ |
| Metallicity [Fe/H] | -0.030 dex |
| Stellar Age | 4.070 Gyr |
| Apparent Magnitude | V: 15.585 · G: 15.525 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.062500 AU |
| Orbital Period | 5.743 days |
| Mean Orbital Velocity | 118.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 90.0000° |
| Mean Bulk Density | 1.64 g/cm³ (20.4 km/s vesc) |
| Insolation Flux | 484.5100 S⊕ (~659,418 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 5757.400 LY (1765.230 pc) |