HD 106315 c
Astrophysical Synthesis & Habitability Characterization
HD 106315 c is a confirmed sub-neptune exoplanet orbiting the star HD 106315, located approximately 356.7 light-years (109.35 parsecs) from the Solar System. First announced in 2017 by K2 using the Transit detection technique (producing an estimated primary transit depth of 0.0947% across the stellar disk), this world measures 4.35 Earth radii (0.39 Jupiter radii) and has a measured mass of 15.2 Earth masses. Combining its mass and radius yields a mean bulk density of 1.02 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.8 g⊕ (7.85 m/s²), and an escape velocity of 20.9 km/s.
In its orbital architecture around HD 106315, HD 106315 c completes one full revolution every 21.057 Earth days at a semi-major axis of 0.1536 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 79.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.22 carries the world between 0.1198 AU at periapsis and 0.1874 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 886 K (+613°C / +1135°F) and receiving 97.00 S⊕ (~132,017 W/m²), HD 106315 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 106315 is classified as a warm F-type star of spectral type F5 V with an effective photospheric temperature of 6,327 K, a radius of 1.296 R☉, a mass of 1.091 M☉, an estimated bolometric luminosity of 2.415 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.48 Gyr and a metallicity of [Fe/H] = -0.311 dex (metal-poor relative to the Sun). From Earth, HD 106315 shines at apparent V-band magnitude 8.951 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 106315 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 106315 c sharing its stellar neighborhood alongside HD 106315 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: K2 · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 106315 |
| Spectral Type | F5 V |
| Effective Temp (Teff) | 6,327 K |
| Stellar Radius | 1.2960 R☉ |
| Stellar Mass | 1.0910 M☉ |
| Bolometric Luminosity | 2.415 L☉ |
| Metallicity [Fe/H] | -0.311 dex |
| Stellar Age | 4.480 Gyr |
| Apparent Magnitude | V: 8.951 · G: 8.888 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.153600 AU |
| Orbital Period | 21.057 days |
| Mean Orbital Velocity | 79.4 km/s |
| Orbital Eccentricity (e) | 0.22000 |
| Orbital Inclination (i) | 88.6100° |
| Mean Bulk Density | 1.02 g/cm³ (20.9 km/s vesc) |
| Insolation Flux | 97.0000 S⊕ (~132,017 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 356.700 LY (109.353 pc) |