HD 213885 c
Astrophysical Synthesis & Habitability Characterization
HD 213885 c is a confirmed sub-neptune exoplanet orbiting the star HD 213885, located approximately 156.8 light-years (48.09 parsecs) from the Solar System. First announced in 2019 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.71 Earth radii (0.42 Jupiter radii) and has a measured mass of 19.95 Earth masses. Combining its mass and radius yields a mean bulk density of 1.05 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.9 g⊕ (8.83 m/s²), and an escape velocity of 23 km/s.
In its orbital architecture around HD 213885, HD 213885 c completes one full revolution every 4.785 Earth days at a semi-major axis of 0.056798 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 129.1 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 1265 K (+992°C / +1818°F) and receiving 426.53 S⊕ (~580,511 W/m²), HD 213885 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 213885 is classified as a solar-type yellow star of spectral type G with an effective photospheric temperature of 5,978 K, a radius of 1.1011 R☉, a mass of 1.068 M☉, an estimated bolometric luminosity of 1.389 L☉. Stellar evolution modeling indicates an estimated stellar age of 3.8 Gyr and a metallicity of [Fe/H] = -0.04 dex (near-solar heavy-element abundance). From Earth, HD 213885 shines at apparent V-band magnitude 7.95 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 213885 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 213885 c sharing its stellar neighborhood alongside HD 213885 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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 213885 |
| Spectral Type | G |
| Effective Temp (Teff) | 5,978 K |
| Stellar Radius | 1.1011 R☉ |
| Stellar Mass | 1.0680 M☉ |
| Bolometric Luminosity | 1.389 L☉ |
| Metallicity [Fe/H] | -0.040 dex |
| Stellar Age | 3.800 Gyr |
| Apparent Magnitude | V: 7.950 · G: 7.802 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.056798 AU |
| Orbital Period | 4.785 days |
| Mean Orbital Velocity | 129.1 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.05 g/cm³ (23 km/s vesc) |
| Insolation Flux | 426.5327 S⊕ (~580,511 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 156.800 LY (48.088 pc) |