HIP 12961 b
Astrophysical Synthesis & Habitability Characterization
HIP 12961 b is a confirmed gas giant exoplanet orbiting the star HIP 12961, located approximately 76.2 light-years (23.37 parsecs) from the Solar System. First announced in 2010 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.2 Earth radii (1.18 Jupiter radii) and has a measured mass of 114.419 Earth masses (0.36 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.27 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.66 g⊕ (6.47 m/s²), and an escape velocity of 32.9 km/s.
In its orbital architecture around HIP 12961, HIP 12961 b completes one full revolution every 57.435 Earth days at a semi-major axis of 0.25 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 47.4 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.17 carries the world between 0.2075 AU at periapsis and 0.2925 AU at apoapsis, driving measurable seasonal insolation cycles.
☁️ Atmospheric Regime (Volatile / Gas Envelope): With a radius of 13.200 R⊕, HIP 12961 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 HIP 12961 is classified as a low-mass red dwarf of spectral type M0 with an effective photospheric temperature of 3,901 K, a radius of 0.65 R☉, a mass of 0.69 M☉, an estimated bolometric luminosity of 0.088 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.14 dex (metal-poor relative to the Sun). From Earth, HIP 12961 shines at apparent V-band magnitude 10.25 (faint and requiring research-grade or CCD telescopic photometry) 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 | HIP 12961 |
| Spectral Type | M0 |
| Effective Temp (Teff) | 3,901 K |
| Stellar Radius | 0.6500 R☉ |
| Stellar Mass | 0.6900 M☉ |
| Bolometric Luminosity | 0.088 L☉ |
| Metallicity [Fe/H] | -0.140 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 10.250 · G: 9.599 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.250000 AU |
| Orbital Period | 57.435 days |
| Mean Orbital Velocity | 47.4 km/s |
| Orbital Eccentricity (e) | 0.17000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.27 g/cm³ (32.9 km/s vesc) |
| Insolation Flux | 1.5889 S⊕ (~2,162 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 76.200 LY (23.371 pc) |