GJ 687 c
Astrophysical Synthesis & Habitability Characterization
GJ 687 c is a confirmed sub-neptune exoplanet orbiting the star GJ 687, located approximately 14.8 light-years (4.55 parsecs) from the Solar System. First announced in 2020 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 4.14 Earth radii (0.37 Jupiter radii) and has a measured mass of 16 Earth masses. Combining its mass and radius yields a mean bulk density of 1.24 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.93 g⊕ (9.12 m/s²), and an escape velocity of 22 km/s.
In its orbital architecture around GJ 687, GJ 687 c completes one full revolution every 727.562 Earth days (1.99Julian years) at a semi-major axis of 1.165 AU (comparable to the inner terrestrial zone between Venus, Earth at 1.00 AU, and Mars at 1.52 AU). Its mean orbital velocity is approximately 17.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.4, swinging from 0.699 AU at periapsis out to 1.631 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 99 K (-174°C / -281°F) and an incident flux of 0.02 S⊕ (~21 W/m²), surface water and volatile species on GJ 687 c would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star GJ 687 is classified as a low-mass red dwarf of spectral type M3.0V with an effective photospheric temperature of 3,413 K, a radius of 0.4183 R☉, a mass of 0.4 M☉, an estimated bolometric luminosity of 0.021 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.063 dex (metal-rich relative to the Sun). From Earth, GJ 687 shines at apparent V-band magnitude 9.15 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The GJ 687 system is a multi-planet architecture hosting 2 confirmed worlds, with GJ 687 c sharing its stellar neighborhood alongside GJ 687 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 | GJ 687 |
| Spectral Type | M3.0V |
| Effective Temp (Teff) | 3,413 K |
| Stellar Radius | 0.4183 R☉ |
| Stellar Mass | 0.4000 M☉ |
| Bolometric Luminosity | 0.021 L☉ |
| Metallicity [Fe/H] | 0.063 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.150 · G: 8.028 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.165000 AU |
| Orbital Period | 727.562 days |
| Mean Orbital Velocity | 17.4 km/s |
| Orbital Eccentricity (e) | 0.40000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.24 g/cm³ (22 km/s vesc) |
| Insolation Flux | 0.0157 S⊕ (~21 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 14.800 LY (4.549 pc) |