Key parameters at a glance

A radius of 4.79 Earth radii
A mass of 8.99 Earth masses
Surface gravity around 0.39 g
An orbital period of 8.463 days
Semi-major axis 0.0700 AU
Equilibrium temperature 555 K (282 °C)
Distance from Earth 31.71 light-years
Earth Similarity Index 0.302
Travel time at Voyager 1 speed 559,192 years
Almost certainly tidally locked to its host star given the close orbit

2 siblings around AU Mic

AU Mic b shares its host star with 2 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
AU Mic b this	Neptune-like	4.79	8.99	8.463	555	2020
AU Mic d	Rocky Terrestrial	1.02	1.05	12.736	—	2023
AU Mic c	Sub-Neptune	2.79	14.46	18.859	425	2021

AU Mic b Planet Profile

Physical Specs

Radius

4.79 R⊕

Radius (Jupiter)

0.427 R♃

Mass

8.99 M⊕

Mass (Jupiter)

0.028 M♃

Density

0.49 g/cm³

Surface Gravity

0.39 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.302

HZ Position Inner

Controversial No

Discovery

Year 2020

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#413of 574

top 71.8%

This planet

4.79R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

GJ 581 b 4.79 R⊕ HD 153557 b 4.77 R⊕ Kepler-1527 b 4.77 R⊕

Metric	Earth	AU Mic b	Jupiter
Radius (R⊕)	1.00	4.79	11.21
Mass (M⊕)	1.00	8.99	317.83
Density (g/cm³)	5.51	0.49	1.33
Surface Gravity (g)	1.00	0.39	2.53
Insolation (S⊕)	1.00	21.20	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	8.990 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	57.209 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 197481

HIP

HIP 102409

TIC

TIC 441420236

Gaia DR2

Gaia DR2 6794047652729201024

Gaia DR3

Gaia DR3 6794047652729201024

System

AU Mic

Percentile among Neptune-like cohort

Radius 4.790 R⊕ · percentile 28 / cohort 574

Mass 8.990 M⊕ · percentile 3 / cohort 574

Orbital period 8.46 d · percentile 33 / cohort 524

Distance 9.72 pc · percentile 2 / cohort 572

ESI 0.302 · percentile 50 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

8.463 days

Semi-major axis

0.0700 AU

Eccentricity

0.070

Inclination

88.39 °

Year Length

A year here lasts approximately 8.46 Earth days (2.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0700 AU.

Transit Fingerprint

Depth

0.249 %

Duration

3.240 h

Impact parameter b

0.502

Rp / R★

0.049900

Transit midpoint (BJD)

2,458,330.3509

Photometric dip

Transit produces a flux drop of 2,490 ppm lasting ≈ 3.24 h.

Extended Orbital Architecture

Planet / star radius ratio

0.049900

Semi-major axis / stellar radius

17.510

Impact parameter (b)

0.502

RV semi-amplitude (K)

3.800 m/s

Transit mid-time (BJD)

2,458,330.3509

Long. of periastron (ω)

-52.00°

Sky-projected obliquity (λ)

-4.70°

Angular separation (arcsec)

7.20000

Eq. Temperature

555K

(282 °C)

Insolation (S⊕)

21.20

Earth = 1.00

Earth Similarity (ESI)

0.302

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Radial velocity

Stellar wobble has been measured spectroscopically.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Plavchan et al. 2020

Instrument

TESS CCD Array

Publication

2020-06

Observation locale

Space

Discovery cohort

Planets confirmed in 2020 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

TOI-700 d · Rocky Terrestrial TOI-237 b · Super-Earth TOI-700 b · Rocky Terrestrial TOI-1266 c · Super-Earth LTT 3780 c · Sub-Neptune TOI-700 c · Sub-Neptune TOI-776 c · Sub-Neptune TOI-942 c · Neptune-like TOI-776 b · Super-Earth TOI-1266 b · Sub-Neptune TOI-540 b · Rocky Terrestrial LHS 1815 b · Rocky Terrestrial

Host System: AU Mic

Spectral Class

M-type red dwarf

Effective Temperature

3,540 K — cooler than the Sun (5,778 K)

Estimated Age

0.02 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.862 R☉

Stellar Mass

0.635 M☉

Metallicity [Fe/H]

0.01

Extended Stellar Properties

Surface gravity (log g)

4.370 dex

Stellar density

1.750 g/cm³

Systemic radial velocity

-6.31 km/s

Rotational v·sin i

9.20 km/s

Rotation period

4.86 days

Metallicity ratio

[Fe/H]

Distance

9.72 parsec

Light-years 31.71 ly

V-band magnitude

8.81 mag

Voyager-speed travel 559,192 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

102.829 mas

Total Proper Motion

456.863 mas/yr

PM Right Ascension

281.42 mas/yr

PM Declination

-359.90 mas/yr

Galactic Cartesian (pc)

x = 0.564 · y = -0.642 · z = -0.520

Equatorial (J2000)

RA 311.29114° · Dec -31.34245°

Galactic ℓ, b

12.653° · -36.804°

Ecliptic λ, β

305.307° · -12.825°

HTM-20 index

1266543779

Observation Record

Photometric series

Stellar spectra

Archive notes