AU Mic b
Astrophysical Synthesis & Habitability Characterization
AU Mic b is a confirmed sub-neptune exoplanet orbiting the star AU Mic, located approximately 31.7 light-years (9.72 parsecs) from the Solar System. First announced in 2020 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.2595% across the stellar disk), this world measures 4.79 Earth radii (0.43 Jupiter radii) and has a measured mass of 8.99 Earth masses. Combining its mass and radius yields a mean bulk density of 0.45 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 0.39 g⊕ (3.82 m/s²), and an escape velocity of 15.3 km/s.
In its orbital architecture around AU Mic, AU Mic b completes one full revolution every 8.463 Earth days at a semi-major axis of 0.07 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 90 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.07 carries the world between 0.0651 AU at periapsis and 0.0749 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 555 K (+282°C / +540°F) and receiving 21.20 S⊕ (~28,853 W/m²), AU Mic b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star AU Mic is classified as a low-mass red dwarf of spectral type M1 V with an effective photospheric temperature of 3,540 K, a radius of 0.862 R☉, a mass of 0.635 M☉, an estimated bolometric luminosity of 0.105 L☉. Stellar evolution modeling indicates an estimated stellar age of 0.019 Gyr and a metallicity of [Fe/H] = 0.01 dex (near-solar heavy-element abundance). From Earth, AU Mic shines at apparent V-band magnitude 8.81 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The AU Mic system is a multi-planet architecture hosting 4 confirmed worlds, with AU Mic b sharing its stellar neighborhood alongside AU Mic d, AU Mic c, AU Mic e.
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: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | AU Mic |
| Spectral Type | M1 V |
| Effective Temp (Teff) | 3,540 K |
| Stellar Radius | 0.8620 R☉ |
| Stellar Mass | 0.6350 M☉ |
| Bolometric Luminosity | 0.105 L☉ |
| Metallicity [Fe/H] | 0.010 dex |
| Stellar Age | 0.019 Gyr |
| Apparent Magnitude | V: 8.810 · G: 7.840 |
| System Architecture | 1 Star, 4 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.070000 AU |
| Orbital Period | 8.463 days |
| Mean Orbital Velocity | 90 km/s |
| Orbital Eccentricity (e) | 0.07000 |
| Orbital Inclination (i) | 88.3900° |
| Mean Bulk Density | 0.45 g/cm³ (15.3 km/s vesc) |
| Insolation Flux | 21.2000 S⊕ (~28,853 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 31.700 LY (9.722 pc) |