HD 21411 b
Astrophysical Synthesis & Habitability Characterization
HD 21411 b is a confirmed gas giant exoplanet orbiting the star HD 21411, located approximately 95 light-years (29.13 parsecs) from the Solar System. First announced in 2019 by Las Campanas Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 9.52 Earth radii (0.85 Jupiter radii) and has a measured mass of 65.9 Earth masses (0.21 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.42 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.73 g⊕ (7.16 m/s²), and an escape velocity of 29.4 km/s.
In its orbital architecture around HD 21411, HD 21411 b completes one full revolution every 84.288 Earth days at a semi-major axis of 0.362 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 46.7 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.4, swinging from 0.2172 AU at periapsis out to 0.5068 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 408 K (+135°C / +275°F) and receiving 4.14 S⊕ (~5,630 W/m²), HD 21411 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 21411 is classified as a solar-type yellow star of spectral type G8 V with an effective photospheric temperature of 5,605 K, a radius of 0.8256 R☉, a mass of 0.89 M☉, an estimated bolometric luminosity of 0.604 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.265 dex (metal-poor relative to the Sun). From Earth, HD 21411 shines at apparent V-band magnitude 7.88 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere.
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: Las Campanas Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 21411 |
| Spectral Type | G8 V |
| Effective Temp (Teff) | 5,605 K |
| Stellar Radius | 0.8256 R☉ |
| Stellar Mass | 0.8900 M☉ |
| Bolometric Luminosity | 0.604 L☉ |
| Metallicity [Fe/H] | -0.265 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 7.880 · G: 7.682 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.362000 AU |
| Orbital Period | 84.288 days |
| Mean Orbital Velocity | 46.7 km/s |
| Orbital Eccentricity (e) | 0.40000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.42 g/cm³ (29.4 km/s vesc) |
| Insolation Flux | 4.1365 S⊕ (~5,630 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 95.000 LY (29.133 pc) |