HIP 111909 c
Astrophysical Synthesis & Habitability Characterization
HIP 111909 c is a confirmed gas giant exoplanet orbiting the star HIP 111909, located approximately 287.3 light-years (88.08 parsecs) from the Solar System. First announced in 2025 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 13.9 Earth radii (1.24 Jupiter radii) and has a measured mass of 257.441 Earth masses (0.81 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.53 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.33 g⊕ (13.04 m/s²), and an escape velocity of 48.1 km/s.
In its orbital architecture around HIP 111909, HIP 111909 c completes one full revolution every 893.63 Earth days (2.45Julian years) at a semi-major axis of 1.97 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 24 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 358 K (+85°C / +185°F) and receiving 2.70 S⊕ (~3,672 W/m²), HIP 111909 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star HIP 111909 is classified as an orange K-type star of spectral type K1 III with an effective photospheric temperature of 4,891 K, a radius of 4.53 R☉, a mass of 1.28 M☉, an estimated bolometric luminosity of 10.536 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.3 Gyr and a metallicity of [Fe/H] = -0.01 dex (near-solar heavy-element abundance). From Earth, HIP 111909 shines at apparent V-band magnitude 7.37 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HIP 111909 system is a multi-planet architecture hosting 2 confirmed worlds, with HIP 111909 c sharing its stellar neighborhood alongside HIP 111909 b.
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: Multiple Observatories · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HIP 111909 |
| Spectral Type | K1 III |
| Effective Temp (Teff) | 4,891 K |
| Stellar Radius | 4.5300 R☉ |
| Stellar Mass | 1.2800 M☉ |
| Bolometric Luminosity | 10.536 L☉ |
| Metallicity [Fe/H] | -0.010 dex |
| Stellar Age | 4.300 Gyr |
| Apparent Magnitude | V: 7.370 · G: 7.097 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.970000 AU |
| Orbital Period | 893.63 days |
| Mean Orbital Velocity | 24 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.53 g/cm³ (48.1 km/s vesc) |
| Insolation Flux | 2.6982 S⊕ (~3,672 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 287.300 LY (88.077 pc) |