HD 13808 c
Astrophysical Synthesis & Habitability Characterization
HD 13808 c is a confirmed sub-neptune exoplanet orbiting the star HD 13808, located approximately 92.1 light-years (28.23 parsecs) from the Solar System. First announced in 2021 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.13 Earth radii (0.28 Jupiter radii) and has a measured mass of 9.96 Earth masses. Combining its mass and radius yields a mean bulk density of 1.79 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.02 g⊕ (10 m/s²), and an escape velocity of 20 km/s.
In its orbital architecture around HD 13808, HD 13808 c completes one full revolution every 53.753 Earth days at a semi-major axis of 0.2554 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 51.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.156 carries the world between 0.2156 AU at periapsis and 0.2952 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 425 K (+152°C / +306°F) and receiving 5.64 S⊕ (~7,671 W/m²), HD 13808 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 13808 is classified as an orange K-type star of spectral type K2 V with an effective photospheric temperature of 5,035 K, a radius of 0.781 R☉, a mass of 0.771 M☉, an estimated bolometric luminosity of 0.352 L☉. Stellar evolution modeling indicates an estimated stellar age of 7.2 Gyr and a metallicity of [Fe/H] = -0.21 dex (metal-poor relative to the Sun). From Earth, HD 13808 shines at apparent V-band magnitude 8.36 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 13808 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 13808 c sharing its stellar neighborhood alongside HD 13808 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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 13808 |
| Spectral Type | K2 V |
| Effective Temp (Teff) | 5,035 K |
| Stellar Radius | 0.7810 R☉ |
| Stellar Mass | 0.7710 M☉ |
| Bolometric Luminosity | 0.352 L☉ |
| Metallicity [Fe/H] | -0.210 dex |
| Stellar Age | 7.200 Gyr |
| Apparent Magnitude | V: 8.360 · G: 8.110 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.255400 AU |
| Orbital Period | 53.753 days |
| Mean Orbital Velocity | 51.7 km/s |
| Orbital Eccentricity (e) | 0.15600 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.79 g/cm³ (20 km/s vesc) |
| Insolation Flux | 5.6365 S⊕ (~7,671 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 92.100 LY (28.231 pc) |