HD 15906 c
Astrophysical Synthesis & Habitability Characterization
HD 15906 c is a confirmed sub-neptune exoplanet orbiting the star HD 15906, located approximately 148.6 light-years (45.56 parsecs) from the Solar System. First announced in 2023 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.1243% across the stellar disk), this world measures 2.93 Earth radii and has a measured mass of 8.91 Earth masses. Combining its mass and radius yields a mean bulk density of 1.95 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.04 g⊕ (10.2 m/s²), and an escape velocity of 19.5 km/s.
In its orbital architecture around HD 15906, HD 15906 c completes one full revolution every 21.583 Earth days at a semi-major axis of 0.141 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 71.1 km/s (compared to Earth's 29.8 km/s). With a near-circular eccentricity of e = 0.04 (ranging from 0.1354 AU at periapsis to 0.1466 AU at apoapsis), the planet experiences minimal orbital distance variation.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 532 K (+259°C / +498°F) and receiving 13.37 S⊕ (~18,197 W/m²), HD 15906 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 15906 is classified as an orange K-type star of spectral type K V with an effective photospheric temperature of 4,757 K, a radius of 0.762 R☉, a mass of 0.79 M☉, an estimated bolometric luminosity of 0.267 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.02 dex (near-solar heavy-element abundance). From Earth, HD 15906 shines at apparent V-band magnitude 9.78 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 15906 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 15906 c sharing its stellar neighborhood alongside HD 15906 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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 15906 |
| Spectral Type | K V |
| Effective Temp (Teff) | 4,757 K |
| Stellar Radius | 0.7620 R☉ |
| Stellar Mass | 0.7900 M☉ |
| Bolometric Luminosity | 0.267 L☉ |
| Metallicity [Fe/H] | 0.020 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.780 · G: 9.477 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.141000 AU |
| Orbital Period | 21.583 days |
| Mean Orbital Velocity | 71.1 km/s |
| Orbital Eccentricity (e) | 0.04000 |
| Orbital Inclination (i) | 88.7500° |
| Mean Bulk Density | 1.95 g/cm³ (19.5 km/s vesc) |
| Insolation Flux | 13.3700 S⊕ (~18,197 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 148.600 LY (45.562 pc) |