Key parameters at a glance

A radius of 2.79 Earth radii
A mass of 14.46 Earth masses
Surface gravity around 1.86 g
An orbital period of 18.859 days
Semi-major axis 0.1190 AU
Equilibrium temperature 425 K (152 °C)
Distance from Earth 31.71 light-years
Earth Similarity Index 0.592
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 c 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	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 this	Sub-Neptune	2.79	14.46	18.859	425	2021

AU Mic c Planet Profile

Physical Specs

Radius

2.79 R⊕

Radius (Jupiter)

0.249 R♃

Mass

14.46 M⊕

Mass (Jupiter)

0.046 M♃

Density

3.90 g/cm³

Surface Gravity

1.86 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.592

HZ Position Inner

Controversial No

Discovery

Year 2021

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#754of 1978

top 38.1%

This planet

2.79R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

GJ 3082 b 2.79 R⊕ Kepler-150 d 2.79 R⊕ Kepler-192 c 2.79 R⊕

Metric	Earth	AU Mic c	Jupiter
Radius (R⊕)	1.00	2.79	11.21
Mass (M⊕)	1.00	14.46	317.83
Density (g/cm³)	5.51	3.90	1.33
Surface Gravity (g)	1.00	1.86	2.53
Insolation (S⊕)	1.00	7.30	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	14.460 M⊕	Direct mass measurement (not derived).

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 Sub-Neptune cohort

Radius 2.790 R⊕ · percentile 61 / cohort 1978

Mass 14.460 M⊕ · percentile 92 / cohort 1978

Orbital period 18.86 d · percentile 60 / cohort 1946

Distance 9.72 pc · percentile 1 / cohort 1975

ESI 0.592 · percentile 81 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

18.859 days

Semi-major axis

0.1190 AU

Eccentricity

0.180

Inclination

89.46 °

Year Length

A year here lasts approximately 18.86 Earth days (5.2% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1190 AU.

Transit Fingerprint

Depth

0.085 %

Duration

4.290 h

Impact parameter b

0.259

Rp / R★

0.029100

Transit midpoint (BJD)

2,458,342.2233

Photometric dip

Transit produces a flux drop of 850 ppm lasting ≈ 4.29 h.

Extended Orbital Architecture

Planet / star radius ratio

0.029100

Semi-major axis / stellar radius

29.870

Impact parameter (b)

0.259

RV semi-amplitude (K)

4.696 m/s

Transit mid-time (BJD)

2,458,342.2233

Long. of periastron (ω)

72.80°

Angular separation (arcsec)

12.20000

Eq. Temperature

425K

(152 °C)

Insolation (S⊕)

7.30

Earth = 1.00

Earth Similarity (ESI)

0.592

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

Martioli et al. 2021

Instrument

TESS CCD Array

Publication

2021-05

Observation locale

Space

Discovery cohort

Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

TOI-2257 b · Sub-Neptune TOI-2285 b · Super-Earth TOI-1231 b · Sub-Neptune LHS 1678 c · Rocky Terrestrial LHS 1478 b · Rocky Terrestrial TOI-2406 b · Sub-Neptune HD 207897 b · Sub-Neptune TOI-269 b · Sub-Neptune TIC 172900988 b · Gas Giant TOI-178 g · Sub-Neptune TOI-2076 d · Sub-Neptune TOI-1749 d · Sub-Neptune

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