GJ 720 A b
Astrophysical Synthesis & Habitability Characterization
GJ 720 A b is a confirmed sub-neptune exoplanet orbiting the star GJ 720 A, located approximately 50.7 light-years (15.56 parsecs) from the Solar System. First announced in 2021 by Roque de los Muchachos Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 3.77 Earth radii (0.34 Jupiter radii) and has a measured mass of 13.64 Earth masses. Combining its mass and radius yields a mean bulk density of 1.4 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.96 g⊕ (9.41 m/s²), and an escape velocity of 21.3 km/s.
In its orbital architecture around GJ 720 A, GJ 720 A b completes one full revolution every 19.466 Earth days at a semi-major axis of 0.119 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 66.5 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.12 carries the world between 0.1047 AU at periapsis and 0.1333 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 401 K (+128°C / +262°F) and receiving 4.28 S⊕ (~5,831 W/m²), GJ 720 A b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 720 A is classified as a low-mass red dwarf of spectral type M0.5 V with an effective photospheric temperature of 3,837 K, a radius of 0.56 R☉, a mass of 0.57 M☉, an estimated bolometric luminosity of 0.061 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.14 dex (metal-poor relative to the Sun). From Earth, GJ 720 A shines at apparent V-band magnitude 9.84 (accessible to binoculars and small amateur telescopes) 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: Roque de los Muchachos Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 720 A |
| Spectral Type | M0.5 V |
| Effective Temp (Teff) | 3,837 K |
| Stellar Radius | 0.5600 R☉ |
| Stellar Mass | 0.5700 M☉ |
| Bolometric Luminosity | 0.061 L☉ |
| Metallicity [Fe/H] | -0.140 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.840 · G: 9.105 |
| System Architecture | 2 Stars, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.119000 AU |
| Orbital Period | 19.466 days |
| Mean Orbital Velocity | 66.5 km/s |
| Orbital Eccentricity (e) | 0.12000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.4 g/cm³ (21.3 km/s vesc) |
| Insolation Flux | 4.2846 S⊕ (~5,831 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 50.700 LY (15.558 pc) |