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Entering orbit…
Habitability
7/ 100
Uninhabitable

Reading AU Mic b’s atmosphere

Dominant elements: H, O, He, Si, C, NThis is what a telescope would measure while AU Mic b crosses in front of its star: starlight passes through the atmosphere and spreads into a rainbow band. Each dark line marks a wavelength the atmosphere absorbed.Every element absorbs its own signature wavelengths — hydrogen always darkens the same two spots, calcium another pair, and so on. Astronomers match the lines in a real spectrum against a library of these signatures to say what an atmosphere is made of, light-years away, without ever visiting. A deeper line generally means more of that element is present.AU Mic b sits about 32 light-years away, found by the transit method. Most catalogued distances trace back to parallax: as Earth orbits the Sun, a nearby star appears to shift very slightly against the distant background stars, and the size of that shift gives its distance directly.

AU Mic b

Gas GiantUninhabitable32 light years awayFound 2020

AU Mic b, from the NASA Exoplanet Archive (found 2020). Measured: 8.99 Earth masses, 0.07 AU, a 3540 K M-type star. Composition inferred from a measured bulk density of 0.08x Earth's, larger than even a pure water/ice world of this mass, suggesting a water-rich interior under roughly a 37% hydrogen/helium envelope by mass, with a day locked to its 8.5-day year, as anything orbiting this close would be.

Host star

AU Mic

Type
M-type (Red Dwarf)
Spectral type
M1 V
Temperature
3,540 K
Radius
0.862 ☉
Mass
0.635 ☉
Known planets
4, including this one
Luminosity
0.105 ☉

Published by the NASA Exoplanet Archive. This world’s temperature and habitability score are computed from this star’s measured luminosity, not from a stand-in for its class.

Gas Giant

Magnetic FieldExtreme Activity
Why is this a Gas Giant?Your planet has 66.0% hydrogen and helium, combined with a mass of 9.0x Earth, which exceeds the gas giant threshold.
Gas giants form when massive cores capture enormous atmospheres of light gases. They typically form beyond the 'frost line' where volatiles can condense.
Classification Criteria:
✓ Hydrogen + Helium: 66.0% (>60% required)✓ Mass: 9.0x Earth (>10x required)
Further reading
Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.Envisioning ExoplanetsMichael CarrollWhat these worlds might look like from the ground, painted from the same measurements this page renders.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.
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Habitability ScoreUninhabitable
7
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere18
Hydrogen-rich atmosphere typical of gas giants (partially stripped by slow rotation)
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - extreme temperature swings between eternal day and night sides

Physical Properties

Mass
8.99x Earth (5.37e+25 kg)
Radius
2.08x Earth (13,247 km)
This planet: 2.08× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.08x Earth (20.4 m/s²)
Surface Temperature
614 K (341 °C / 646 °F)
Rotation Period
203.0 hours/day (slower than Earth)
This planet: 203 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.07 AU (10.5 million km)
Orbital Period
12 days

Atmosphere

Hydrogen and helium dominated with trace methane and ammonia

Elemental Composition

H - Hydrogen
54.5%
O - Oxygen
21.3%
He - Helium
11.5%

Surface Characteristics

No solid surface - thick gaseous envelope with possible rocky core deep within
A binary star system's orrery: two suns close together, a red dashed dead-zone boundary, and a debris trail left by a destroyed world

New: Binary Star Systems 🌀

A system can now orbit two suns. Add a companion star when you build one — close, medium, or wide — and the physics decides what survives: a shared center of mass carves out a dead zone where gravity from both stars tears a world apart, leaving it as debris, and every surviving planet's orbit goes elliptical, moving fastest at closest approach and slowest out at aphelion. Push the separation to wide and the dead zone opens tens of AU across, wide enough to gut a system that would have been stable around one star alone. Stand on a world that made it through and you'll watch two suns cross the sky together.

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