AU Mic b
AU Mic b is a Neptune-like planet orbiting the M1 V star AU Mic in the constellation Microscopium. It lies about 32 light-years from Earth and was discovered in 2020 using the transit method.
How Big Is AU Mic b?
AU Mic b has a radius of 4.79 times that of Earth. Its mass is 9.0 times that of Earth, giving it a density of 0.49 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is AU Mic b in the Habitable Zone?
AU Mic b orbits inside the inner edge of the habitable zone of AU Mic. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of AU Mic: 0.265–0.687 AU (conservative: 0.336–0.651 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on AU Mic b
The equilibrium temperature of AU Mic b is about 555 K (282 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on AU Mic b — one full orbit around AU Mic — lasts 8.46 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.070 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.07).
How Was AU Mic b Discovered?
AU Mic b was discovered in 2020 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is AU Mic b?
AU Mic b is 31.7 light-years (9.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1995. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 557,920 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. AU Mic b scores 0.22, ranking #3,614 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: AU Mic
AU Mic
- Spectral type
- M1 V
- Surface temperature
- 3,540 K (Sun: 5,772 K)
- Mass
- 0.64 M☉
- Radius
- 0.86 R☉
- Luminosity
- 0.1053 L☉
- Age
- 0.0 billion years (Sun: 4.6)
The AU Mic Planetary System
AU Mic b is one of 4 known planets in the AU Mic system. Its siblings:
AU Mic b — Complete Data
| Radius | 4.790 Earth radii (0.427 Jupiter radii) |
|---|---|
| Mass | 8.99 Earth masses (0.028 Jupiter masses) |
| Density | 0.49 g/cm³ (Earth: 5.51) |
| Orbital period | 8.46 days |
| Orbital distance | 0.070 AU |
| Eccentricity | 0.070 |
| Equilibrium temperature | 555 K (282 °C) |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 31.7 light-years (9.7 parsecs) |
| Constellation | Microscopium |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2020 |
Data: NASA Exoplanet Archive, last updated 2026-03-05. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About AU Mic b
Is AU Mic b habitable?
No — AU Mic b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is AU Mic b?
AU Mic b is about 32 light-years from Earth in the constellation Microscopium. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 557,920 years to get there.
How big is AU Mic b compared to Earth?
AU Mic b has 4.79 times the radius of Earth and about 9.0 times its mass.
How long is a year on AU Mic b?
One orbit around AU Mic takes 8.5 Earth days — short enough that 43 of its years would fit into one Earth year.
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