HAT-P-11 c
Astrophysical Synthesis & Habitability Characterization
HAT-P-11 c is a confirmed gas giant exoplanet orbiting the star HAT-P-11, located approximately 123.2 light-years (37.77 parsecs) from the Solar System. First announced in 2018 by W. M. Keck 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 851.78 Earth masses (2.68 Jupiter masses). Combining its mass and radius yields a mean bulk density of 2.04 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 4.89 g⊕ (47.95 m/s²), and an escape velocity of 89.9 km/s.
In its orbital architecture around HAT-P-11, HAT-P-11 c completes one full revolution every 3361 Earth days (9.2Julian years) at a semi-major axis of 4.1 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 13.3 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.652, swinging from 1.4268 AU at periapsis out to 6.7732 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 92 K (-181°C / -294°F) and an incident flux of 0.02 S⊕ (~22 W/m²), surface water and volatile species on HAT-P-11 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star HAT-P-11 is classified as an orange K-type star of spectral type K4 with an effective photospheric temperature of 4,653 K, a radius of 0.683 R☉, a mass of 0.811 M☉, an estimated bolometric luminosity of 0.196 L☉. Stellar evolution modeling indicates an estimated stellar age of 2.69 Gyr and a metallicity of [Fe/H] = 0.31 dex (metal-rich relative to the Sun). From Earth, HAT-P-11 shines at apparent V-band magnitude 9.46 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The HAT-P-11 system is a multi-planet architecture hosting 2 confirmed worlds, with HAT-P-11 c sharing its stellar neighborhood alongside HAT-P-11 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: W. M. Keck Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | HAT-P-11 |
| Spectral Type | K4 |
| Effective Temp (Teff) | 4,653 K |
| Stellar Radius | 0.6830 R☉ |
| Stellar Mass | 0.8110 M☉ |
| Bolometric Luminosity | 0.196 L☉ |
| Metallicity [Fe/H] | 0.310 dex |
| Stellar Age | 2.690 Gyr |
| Apparent Magnitude | V: 9.460 · G: 9.151 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 4.100000 AU |
| Orbital Period | 3361 days |
| Mean Orbital Velocity | 13.3 km/s |
| Orbital Eccentricity (e) | 0.65200 |
| Orbital Inclination (i) | 33.1000° |
| Mean Bulk Density | 2.04 g/cm³ (89.9 km/s vesc) |
| Insolation Flux | 0.0161 S⊕ (~22 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 123.200 LY (37.765 pc) |