Kepler-9 c
Astrophysical Synthesis & Habitability Characterization
Kepler-9 c is a confirmed gas giant exoplanet orbiting the star Kepler-9, located approximately 2049.1 light-years (628.26 parsecs) from the Solar System. First announced in 2010 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.5979% across the stellar disk), this world measures 8.08 Earth radii (0.72 Jupiter radii) and has a measured mass of 29.9 Earth masses. Combining its mass and radius yields a mean bulk density of 0.31 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.46 g⊕ (4.51 m/s²), and an escape velocity of 21.5 km/s.
In its orbital architecture around Kepler-9, Kepler-9 c completes one full revolution every 38.985 Earth days at a semi-major axis of 0.227 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 63.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.06691 carries the world between 0.2118 AU at periapsis and 0.2422 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 523 K (+250°C / +482°F) and receiving 18.90 S⊕ (~25,727 W/m²), Kepler-9 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-9 is classified as a stellar host with an effective photospheric temperature of 5,774 K, a radius of 0.958 R☉, a mass of 1.022 M☉, an estimated bolometric luminosity of 0.915 L☉. Stellar evolution modeling indicates an estimated stellar age of 2 Gyr and a metallicity of [Fe/H] = 0.05 dex (near-solar heavy-element abundance). From Earth, Kepler-9 shines at apparent V-band magnitude 13.922 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-9 system is a multi-planet architecture hosting 3 confirmed worlds, with Kepler-9 c sharing its stellar neighborhood alongside Kepler-9 d, Kepler-9 b.
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-9 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,774 K |
| Stellar Radius | 0.9580 R☉ |
| Stellar Mass | 1.0220 M☉ |
| Bolometric Luminosity | 0.915 L☉ |
| Metallicity [Fe/H] | 0.050 dex |
| Stellar Age | 2.000 Gyr |
| Apparent Magnitude | V: 13.922 · G: 13.781 |
| System Architecture | 1 Star, 3 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.227000 AU |
| Orbital Period | 38.985 days |
| Mean Orbital Velocity | 63.3 km/s |
| Orbital Eccentricity (e) | 0.06691 |
| Orbital Inclination (i) | 89.1880° |
| Mean Bulk Density | 0.31 g/cm³ (21.5 km/s vesc) |
| Insolation Flux | 18.9030 S⊕ (~25,727 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2049.100 LY (628.257 pc) |