Kepler-173 c
Astrophysical Synthesis & Habitability Characterization
Kepler-173 c is a confirmed sub-neptune exoplanet orbiting the star Kepler-173, located approximately 2717.4 light-years (833.17 parsecs) from the Solar System. First announced in 2014 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0551% across the stellar disk), this world measures 2.43 Earth radii and has a measured mass of 6.48 Earth masses. Combining its mass and radius yields a mean bulk density of 2.49 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.1 g⊕ (10.79 m/s²), and an escape velocity of 18.3 km/s.
In its orbital architecture around Kepler-173, Kepler-173 c completes one full revolution every 8.006 Earth days at a semi-major axis of 0.074 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 100.6 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 956 K (+683°C / +1261°F) and receiving 258.42 S⊕ (~351,707 W/m²), Kepler-173 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-173 is classified as a stellar host with an effective photospheric temperature of 6,031 K, a radius of 0.949 R☉, a mass of 1.067 M☉, an estimated bolometric luminosity of 1.069 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.3 Gyr and a metallicity of [Fe/H] = 0.036 dex (near-solar heavy-element abundance). From Earth, Kepler-173 shines at apparent V-band magnitude 14.357 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere. The Kepler-173 system is a multi-planet architecture hosting 2 confirmed worlds, with Kepler-173 c sharing its stellar neighborhood alongside Kepler-173 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-173 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 6,031 K |
| Stellar Radius | 0.9490 R☉ |
| Stellar Mass | 1.0670 M☉ |
| Bolometric Luminosity | 1.069 L☉ |
| Metallicity [Fe/H] | 0.036 dex |
| Stellar Age | 3.300 Gyr |
| Apparent Magnitude | V: 14.357 · G: 14.258 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.074000 AU |
| Orbital Period | 8.006 days |
| Mean Orbital Velocity | 100.6 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7400° |
| Mean Bulk Density | 2.49 g/cm³ (18.3 km/s vesc) |
| Insolation Flux | 258.4180 S⊕ (~351,707 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2717.400 LY (833.165 pc) |