HD 213240 b
Astrophysical Synthesis & Habitability Characterization
HD 213240 b is a confirmed gas giant exoplanet orbiting the star HD 213240, located approximately 133.3 light-years (40.87 parsecs) from the Solar System. First announced in 2001 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 12.8 Earth radii (1.14 Jupiter radii) and has a measured mass of 1655.886 Earth masses (5.21 Jupiter masses). Combining its mass and radius yields a mean bulk density of 4.35 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 10.11 g⊕ (99.15 m/s²), and an escape velocity of 127.2 km/s.
In its orbital architecture around HD 213240, HD 213240 b completes one full revolution every 882.7 Earth days (2.42Julian years) at a semi-major axis of 1.89 AU (corresponding to the middle-system regime between Mars at 1.52 AU and Jupiter at 5.20 AU). Its mean orbital velocity is approximately 23.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.42, swinging from 1.0962 AU at periapsis out to 2.6838 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 12.800 R⊕, HD 213240 b exceeds the empirical ~1.8–2.2 R⊕ Fulton radius valley threshold, indicating a substantial hydrogen-helium or supercritical volatile envelope without a conventional solid terrestrial surface.
The host star HD 213240 is classified as a solar-type yellow star of spectral type G0/1 V with an effective photospheric temperature of 5,979 K, a radius of 1.51 R☉, a mass of 1.57 M☉, an estimated bolometric luminosity of 2.614 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.6 Gyr and a metallicity of [Fe/H] = 0.15 dex (metal-rich relative to the Sun). From Earth, HD 213240 shines at apparent V-band magnitude 6.81 (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: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 213240 |
| Spectral Type | G0/1 V |
| Effective Temp (Teff) | 5,979 K |
| Stellar Radius | 1.5100 R☉ |
| Stellar Mass | 1.5700 M☉ |
| Bolometric Luminosity | 2.614 L☉ |
| Metallicity [Fe/H] | 0.150 dex |
| Stellar Age | 4.600 Gyr |
| Apparent Magnitude | V: 6.810 · G: 6.658 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.890000 AU |
| Orbital Period | 882.7 days |
| Mean Orbital Velocity | 23.3 km/s |
| Orbital Eccentricity (e) | 0.42000 |
| Orbital Inclination (i) | 63.0000° |
| Mean Bulk Density | 4.35 g/cm³ (127.2 km/s vesc) |
| Insolation Flux | 0.7524 S⊕ (~1,024 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 133.300 LY (40.871 pc) |