HD 20003 b
Astrophysical Synthesis & Habitability Characterization
HD 20003 b is a confirmed sub-neptune exoplanet orbiting the star HD 20003, located approximately 136.4 light-years (41.83 parsecs) from the Solar System. First announced in 2019 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.43 Earth radii (0.31 Jupiter radii) and has a measured mass of 11.66 Earth masses. Combining its mass and radius yields a mean bulk density of 1.59 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.99 g⊕ (9.71 m/s²), and an escape velocity of 20.6 km/s.
In its orbital architecture around HD 20003, HD 20003 b completes one full revolution every 11.848 Earth days at a semi-major axis of 0.0974 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 89.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.36, swinging from 0.0623 AU at periapsis out to 0.1325 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 815 K (+542°C / +1008°F) and receiving 75.90 S⊕ (~103,293 W/m²), HD 20003 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 20003 is classified as a solar-type yellow star of spectral type G8 V with an effective photospheric temperature of 5,494 K, a radius of 0.9216 R☉, a mass of 0.875 M☉, an estimated bolometric luminosity of 0.694 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.04 dex (near-solar heavy-element abundance). From Earth, HD 20003 shines at apparent V-band magnitude 8.39 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 20003 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 20003 b sharing its stellar neighborhood alongside HD 20003 c.
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 20003 |
| Spectral Type | G8 V |
| Effective Temp (Teff) | 5,494 K |
| Stellar Radius | 0.9216 R☉ |
| Stellar Mass | 0.8750 M☉ |
| Bolometric Luminosity | 0.694 L☉ |
| Metallicity [Fe/H] | 0.040 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 8.390 · G: 8.192 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.097400 AU |
| Orbital Period | 11.848 days |
| Mean Orbital Velocity | 89.4 km/s |
| Orbital Eccentricity (e) | 0.36000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.59 g/cm³ (20.6 km/s vesc) |
| Insolation Flux | 75.8952 S⊕ (~103,293 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 136.400 LY (41.832 pc) |