GJ 9773 b
Astrophysical Synthesis & Habitability Characterization
GJ 9773 b is a confirmed gas giant exoplanet orbiting the star GJ 9773, located approximately 51.9 light-years (15.92 parsecs) from the Solar System. First announced in 2025 by Calar Alto Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 14.2 Earth radii (1.27 Jupiter radii) and has a measured mass of 172.581 Earth masses (0.54 Jupiter masses). Combining its mass and radius yields a mean bulk density of 0.33 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.86 g⊕ (8.43 m/s²), and an escape velocity of 39 km/s.
In its orbital architecture around GJ 9773, GJ 9773 b completes one full revolution every 2965 Earth days (8.12Julian years) at a semi-major axis of 2.921 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 10.7 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.218 carries the world between 2.2842 AU at periapsis and 3.5578 AU at apoapsis, driving measurable seasonal insolation cycles.
❄️ Thermal Regime (Cryogenic Zone): With an equilibrium temperature of 60 K (-213°C / -351°F) and an incident flux of 0.00 S⊕ (~3 W/m²), surface water and volatile species on GJ 9773 b would remain locked in cryogenic ice phases unless warmed by subsurface tidal or radiogenic heating.
The host star GJ 9773 is classified as a low-mass red dwarf of spectral type M3.0 V with an effective photospheric temperature of 3,528 K, a radius of 0.362 R☉, a mass of 0.358 M☉, an estimated bolometric luminosity of 0.018 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.2 dex (metal-poor relative to the Sun). From Earth, GJ 9773 shines at apparent V-band magnitude 12.033 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
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: Calar Alto Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 9773 |
| Spectral Type | M3.0 V |
| Effective Temp (Teff) | 3,528 K |
| Stellar Radius | 0.3620 R☉ |
| Stellar Mass | 0.3580 M☉ |
| Bolometric Luminosity | 0.018 L☉ |
| Metallicity [Fe/H] | -0.200 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 12.033 · G: 10.905 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 2.921000 AU |
| Orbital Period | 2965 days |
| Mean Orbital Velocity | 10.7 km/s |
| Orbital Eccentricity (e) | 0.21800 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 0.33 g/cm³ (39 km/s vesc) |
| Insolation Flux | 0.0021 S⊕ (~3 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 51.900 LY (15.921 pc) |