Key parameters at a glance

A radius of 3.25 Earth radii
A mass of 10.60 Earth masses
Surface gravity around 1.00 g
An orbital period of 24.422 days
Semi-major axis 0.1420 AU
Equilibrium temperature 391 K (118 °C)
Distance from Earth 20.65 light-years
Earth Similarity Index 0.550
Travel time at Voyager 1 speed 364,234 years
Almost certainly tidally locked to its host star given the close orbit

GJ 338 B b Planet Profile

Physical Specs

Radius

3.25 R⊕

Radius (Jupiter)

0.290 R♃

Mass

10.60 M⊕

Mass (Jupiter)

0.033 M♃

Density

1.70 g/cm³

Surface Gravity

1.00 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.550

HZ Position Unknown

Controversial No

Discovery

Year 2020

Method Radial Velocity

Facility Calar Alto Observatory

Telescope 3.5 m telescope

Size rank in cohort

Rank by radius

#312of 1978

top 15.7%

This planet

3.25R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-199 c 3.25 R⊕ GJ 163 b 3.25 R⊕ HD 20781 d 3.25 R⊕

Metric	Earth	GJ 338 B b	Jupiter
Radius (R⊕)	1.00	3.25	11.21
Mass (M⊕)	1.00	10.60	317.83
Density (g/cm³)	5.51	1.70	1.33
Surface Gravity (g)	1.00	1.00	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	10.600 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 79211

HIP

HIP 120005

TIC

TIC 251078597

Gaia DR2

Gaia DR2 1022456104850892928

Gaia DR3

Gaia DR3 1022456104850892928

System

GJ 338

Percentile among Sub-Neptune cohort

Radius 3.250 R⊕ · percentile 84 / cohort 1978

Mass 10.600 M⊕ · percentile 77 / cohort 1978

Orbital period 24.42 d · percentile 68 / cohort 1946

Distance 6.33 pc · percentile 1 / cohort 1975

ESI 0.550 · percentile 76 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

24.422 days

Semi-major axis

0.1420 AU

Eccentricity

0.109

Inclination

— °

Year Length

A year here lasts approximately 24.42 Earth days (6.7% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1420 AU.

Extended Orbital Architecture

RV semi-amplitude (K)

3.190 m/s

Transit mid-time (BJD)

2,457,521.4300

Long. of periastron (ω)

204.30°

Angular separation (arcsec)

22.40000

Eq. Temperature

391K

(118 °C)

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.550

0 = alien, 1 = Earth-identical

Insufficient insolation data — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

Discovery Paper

Primary reference

Gonz Aacute Lez Aacute Lvarez et al. 2020

Instrument

CARMENES

Publication

2020-05

Observation locale

Ground

Host System: GJ 338 B

Spectral Class

M-type red dwarf

Effective Temperature

4,014 K — cooler than the Sun (5,778 K)

Estimated Age

4.00 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.580 R☉

Stellar Mass

0.640 M☉

Metallicity [Fe/H]

-0.03

Extended Stellar Properties

Surface gravity (log g)

4.680 dex

Stellar density

4.045 g/cm³

Systemic radial velocity

11.80 km/s

Rotational v·sin i

2.30 km/s

Rotation period

16.61 days

Metallicity ratio

[Fe/H]

Distance

6.33 parsec

Light-years 20.65 ly

V-band magnitude

7.70 mag

Voyager-speed travel 364,234 yr

Multi-band Host Photometry — 7 bands

Astrometric Data

Parallax

157.885 mas

Total Proper Motion

1,706.009 mas/yr

PM Right Ascension

-1,573.12 mas/yr

PM Declination

-660.12 mas/yr

Galactic Cartesian (pc)

x = -0.455 · y = 0.401 · z = 0.795

Equatorial (J2000)

RA 138.59167° · Dec 52.68352°

Galactic ℓ, b

164.940° · 42.666°

Ecliptic λ, β

123.600° · 34.763°

HTM-20 index

353395592