HIP 65407 b
Astrophysical Synthesis & Habitability Characterization
HIP 65407 b is a confirmed gas giant exoplanet orbiting the star HIP 65407, located approximately 201.5 light-years (61.78 parsecs) from the Solar System. First announced in 2016 by Haute-Provence Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.3 Earth radii (1.28 Jupiter radii) and has a measured mass of 136.031 Earth masses (0.43 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.26 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.67 g⊕ (6.57 m/s²), and an escape velocity of 34.5 km/s.
In its orbital architecture around HIP 65407, HIP 65407 b completes one full revolution every 28.125 Earth days at a semi-major axis of 0.177 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 68.5 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.14 carries the world between 0.1522 AU at periapsis and 0.2018 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 611 K (+338°C / +640°F) and receiving 20.80 S⊕ (~28,306 W/m²), HIP 65407 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 65407 is classified as an orange K-type star of spectral type K0 with an effective photospheric temperature of 5,460 K, a radius of 0.9523 R☉, a mass of 0.93 M☉, an estimated bolometric luminosity of 0.723 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.25 dex (metal-rich relative to the Sun). From Earth, HIP 65407 shines at apparent V-band magnitude 9.38 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HIP 65407 system is a multi-planet architecture hosting 2 confirmed worlds, with HIP 65407 b sharing its stellar neighborhood alongside HIP 65407 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: Haute-Provence Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HIP 65407 |
| Spectral Type | K0 |
| Effective Temp (Teff) | 5,460 K |
| Stellar Radius | 0.9523 R☉ |
| Stellar Mass | 0.9300 M☉ |
| Bolometric Luminosity | 0.723 L☉ |
| Metallicity [Fe/H] | 0.250 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.380 · G: 9.151 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.177000 AU |
| Orbital Period | 28.125 days |
| Mean Orbital Velocity | 68.5 km/s |
| Orbital Eccentricity (e) | 0.14000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.26 g/cm³ (34.5 km/s vesc) |
| Insolation Flux | 20.7979 S⊕ (~28,306 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 201.500 LY (61.780 pc) |