HD 1397 b
Astrophysical Synthesis & Habitability Characterization
HD 1397 b is a confirmed gas giant exoplanet orbiting the star HD 1397, located approximately 259.5 light-years (79.57 parsecs) from the Solar System. First announced in 2018 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.2037% across the stellar disk), this world measures 11.5 Earth radii (1.03 Jupiter radii) and has a measured mass of 131.899 Earth masses (0.41 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.48 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1 g⊕ (9.81 m/s²), and an escape velocity of 37.9 km/s.
In its orbital architecture around HD 1397, HD 1397 b completes one full revolution every 11.535 Earth days at a semi-major axis of 0.1097 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 103.5 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.251, swinging from 0.0822 AU at periapsis out to 0.1372 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1228 K (+955°C / +1751°F) and receiving 356.00 S⊕ (~484,516 W/m²), HD 1397 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HD 1397 is classified as a solar-type yellow star of spectral type G5 III/IV with an effective photospheric temperature of 5,521 K, a radius of 2.336 R☉, a mass of 1.324 M☉, an estimated bolometric luminosity of 4.549 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.51 Gyr and a metallicity of [Fe/H] = 0.29 dex (metal-rich relative to the Sun). From Earth, HD 1397 shines at apparent V-band magnitude 7.79 (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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HD 1397 |
| Spectral Type | G5 III/IV |
| Effective Temp (Teff) | 5,521 K |
| Stellar Radius | 2.3360 R☉ |
| Stellar Mass | 1.3240 M☉ |
| Bolometric Luminosity | 4.549 L☉ |
| Metallicity [Fe/H] | 0.290 dex |
| Stellar Age | 4.510 Gyr |
| Apparent Magnitude | V: 7.790 · G: 7.593 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.109700 AU |
| Orbital Period | 11.535 days |
| Mean Orbital Velocity | 103.5 km/s |
| Orbital Eccentricity (e) | 0.25100 |
| Orbital Inclination (i) | 88.9900° |
| Mean Bulk Density | 0.48 g/cm³ (37.9 km/s vesc) |
| Insolation Flux | 356.0000 S⊕ (~484,516 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 259.500 LY (79.570 pc) |