HD 155918 c
Astrophysical Synthesis & Habitability Characterization
HD 155918 c is a confirmed gas giant exoplanet orbiting the star HD 155918, located approximately 89.9 light-years (27.56 parsecs) from the Solar System. First announced in 2022 by Multiple Observatories 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 1878.048 Earth masses (5.91 Jupiter masses). Combining its mass and radius yields a mean bulk density of 4.94 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 11.46 g⊕ (112.38 m/s²), and an escape velocity of 135.5 km/s.
In its orbital architecture around HD 155918, HD 155918 c completes one full revolution every 17202.194 Earth days (47.1Julian years) at a semi-major axis of 13.183 AU (a wide outer-system orbit beyond Jupiter's 5.20 AU distance in our Solar System). Its mean orbital velocity is approximately 8.3 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.071 carries the world between 12.247 AU at periapsis and 14.119 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 77 K (-196°C / -321°F) and an incident flux of 0.01 S⊕ (~8 W/m²), surface water and volatile species on HD 155918 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HD 155918 is classified as a solar-type yellow star of spectral type G2V with an effective photospheric temperature of 5,772 K, a radius of 1.0191 R☉, a mass of 1.03 M☉, an estimated bolometric luminosity of 1.034 L☉. Stellar evolution modeling indicates an estimated stellar age of 12.3 Gyr and a metallicity of [Fe/H] = -0.662 dex (metal-poor relative to the Sun). From Earth, HD 155918 shines at apparent V-band magnitude 7 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The HD 155918 system is a multi-planet architecture hosting 2 confirmed worlds, with HD 155918 c sharing its stellar neighborhood alongside HD 155918 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 | HD 155918 |
| Spectral Type | G2V |
| Effective Temp (Teff) | 5,772 K |
| Stellar Radius | 1.0191 R☉ |
| Stellar Mass | 1.0300 M☉ |
| Bolometric Luminosity | 1.034 L☉ |
| Metallicity [Fe/H] | -0.662 dex |
| Stellar Age | 12.300 Gyr |
| Apparent Magnitude | V: 7.000 · G: 6.841 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 13.183000 AU |
| Orbital Period | 17202.194 days |
| Mean Orbital Velocity | 8.3 km/s |
| Orbital Eccentricity (e) | 0.07100 |
| Orbital Inclination (i) | 31.7710° |
| Mean Bulk Density | 4.94 g/cm³ (135.5 km/s vesc) |
| Insolation Flux | 0.0060 S⊕ (~8 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 89.900 LY (27.561 pc) |