55 Cnc c
Astrophysical Synthesis & Habitability Characterization
55 Cnc c is a confirmed gas giant exoplanet orbiting the star 55 Cnc, located approximately 41 light-years (12.59 parsecs) from the Solar System. First announced in 2004 by McDonald Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 8.51 Earth radii (0.76 Jupiter radii) and has a measured mass of 54.474 Earth masses (0.17 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.49 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.75 g⊕ (7.35 m/s²), and an escape velocity of 28.3 km/s.
In its orbital architecture around 55 Cnc, 55 Cnc c completes one full revolution every 44.394 Earth days at a semi-major axis of 0.247 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 60.5 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.088 carries the world between 0.2253 AU at periapsis and 0.2687 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 499 K (+226°C / +439°F) and receiving 10.41 S⊕ (~14,175 W/m²), 55 Cnc c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star 55 Cnc is classified as a solar-type yellow star of spectral type G8 V with an effective photospheric temperature of 5,198 K, a radius of 0.98 R☉, a mass of 1.015 M☉, an estimated bolometric luminosity of 0.629 L☉. Stellar evolution modeling indicates an estimated stellar age of 10 Gyr and a metallicity of [Fe/H] = 0.39 dex (metal-rich relative to the Sun). From Earth, 55 Cnc shines at apparent V-band magnitude 5.951 (visible to the unaided human eye under dark skies) in the Northern celestial hemisphere. The 55 Cnc system is a multi-planet architecture hosting 5 confirmed worlds, with 55 Cnc c sharing its stellar neighborhood alongside 55 Cnc e, 55 Cnc b, 55 Cnc f, 55 Cnc d.
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: McDonald Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | 55 Cnc |
| Spectral Type | G8 V |
| Effective Temp (Teff) | 5,198 K |
| Stellar Radius | 0.9800 R☉ |
| Stellar Mass | 1.0150 M☉ |
| Bolometric Luminosity | 0.629 L☉ |
| Metallicity [Fe/H] | 0.390 dex |
| Stellar Age | 10.000 Gyr |
| Apparent Magnitude | V: 5.951 · G: 5.730 |
| System Architecture | 2 Stars, 7 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.247000 AU |
| Orbital Period | 44.394 days |
| Mean Orbital Velocity | 60.5 km/s |
| Orbital Eccentricity (e) | 0.08800 |
| Orbital Inclination (i) | 89.7300° |
| Mean Bulk Density | 0.49 g/cm³ (28.3 km/s vesc) |
| Insolation Flux | 10.4149 S⊕ (~14,175 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 41.000 LY (12.586 pc) |