Kepler-729 b
Astrophysical Synthesis & Habitability Characterization
Kepler-729 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-729, located approximately 6265.9 light-years (1921.15 parsecs) from the Solar System. First announced in 2016 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.1301% across the stellar disk), this world measures 3.58 Earth radii (0.32 Jupiter radii) and has a measured mass of 12.5 Earth masses. Combining its mass and radius yields a mean bulk density of 1.5 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.98 g⊕ (9.61 m/s²), and an escape velocity of 20.9 km/s.
In its orbital architecture around Kepler-729, Kepler-729 b completes one full revolution every 3.166 Earth days at a semi-major axis of 0.0432 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 148.4 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 1273 K (+1000°C / +1832°F) and receiving 1,089.55 S⊕ (~1,482,876 W/m²), Kepler-729 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-729 is classified as a stellar host with an effective photospheric temperature of 5,633 K, a radius of 0.91 R☉, a mass of 0.94 M☉, an estimated bolometric luminosity of 0.748 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.27 Gyr and a metallicity of [Fe/H] = -0.05 dex (near-solar heavy-element abundance). From Earth, Kepler-729 shines at apparent V-band magnitude 15.567 (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-729 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,633 K |
| Stellar Radius | 0.9100 R☉ |
| Stellar Mass | 0.9400 M☉ |
| Bolometric Luminosity | 0.748 L☉ |
| Metallicity [Fe/H] | -0.050 dex |
| Stellar Age | 4.270 Gyr |
| Apparent Magnitude | V: 15.567 · G: 15.547 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.043200 AU |
| Orbital Period | 3.166 days |
| Mean Orbital Velocity | 148.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7600° |
| Mean Bulk Density | 1.5 g/cm³ (20.9 km/s vesc) |
| Insolation Flux | 1089.5490 S⊕ (~1,482,876 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 6265.900 LY (1921.150 pc) |