GJ 229 b
Astrophysical Synthesis & Habitability Characterization
GJ 229 b is a confirmed sub-neptune exoplanet orbiting the star GJ 229, located approximately 18.8 light-years (5.76 parsecs) from the Solar System. First announced in 2014 by Multiple Observatories using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.97 Earth radii (0.35 Jupiter radii) and has a measured mass of 14.938 Earth masses. Combining its mass and radius yields a mean bulk density of 1.32 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.95 g⊕ (9.32 m/s²), and an escape velocity of 21.7 km/s.
In its orbital architecture around GJ 229, GJ 229 b completes one full revolution every 579.475 Earth days (1.59Julian years) at a semi-major axis of 1.086 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 20.4 km/s (compared to Earth's 29.8 km/s). The planet follows a highly eccentric trajectory (e = 0.404, swinging from 0.6473 AU at periapsis out to 1.5247 AU at apoapsis), pointing to past dynamical scattering or secular gravitational perturbations.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 112 K (-161°C / -258°F) and an incident flux of 0.02 S⊕ (~32 W/m²), surface water and volatile species on GJ 229 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star GJ 229 is classified as a low-mass red dwarf of spectral type M1.5V with an effective photospheric temperature of 3,564 K, a radius of 0.46 R☉, a mass of 0.509 M☉, an estimated bolometric luminosity of 0.031 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.4 Gyr. From Earth, GJ 229 shines at apparent V-band magnitude 8.15 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The GJ 229 system is a multi-planet architecture hosting 2 confirmed worlds, with GJ 229 b sharing its stellar neighborhood alongside GJ 229 A c.
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 229 |
| Spectral Type | M1.5V |
| Effective Temp (Teff) | 3,564 K |
| Stellar Radius | 0.4600 R☉ |
| Stellar Mass | 0.5090 M☉ |
| Bolometric Luminosity | 0.031 L☉ |
| Metallicity [Fe/H] | — |
| Stellar Age | 0.400 Gyr |
| Apparent Magnitude | V: 8.150 · G: 7.307 |
| System Architecture | 3 Stars, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 1.086000 AU |
| Orbital Period | 579.475 days |
| Mean Orbital Velocity | 20.4 km/s |
| Orbital Eccentricity (e) | 0.40400 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.32 g/cm³ (21.7 km/s vesc) |
| Insolation Flux | 0.0237 S⊕ (~32 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 18.800 LY (5.756 pc) |