Key parameters at a glance

A radius of 1.88 Earth radii
A mass of 4.18 Earth masses
Surface gravity around 1.18 g
An orbital period of 5.974 days
Semi-major axis 0.0570 AU
Distance from Earth 92.86 light-years
Earth Similarity Index 0.808
Travel time at Voyager 1 speed 1,637,595 years
Almost certainly tidally locked to its host star given the close orbit

2 siblings around GJ 3138

GJ 3138 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
GJ 3138 b	Rocky Terrestrial	1.18	1.78	1.220	—	2017
GJ 3138 c this	Super-Earth	1.88	4.18	5.974	—	2017
GJ 3138 d	Sub-Neptune	3.23	10.50	257.800	—	2017

GJ 3138 c Planet Profile

Physical Specs

Radius

1.88 R⊕

Radius (Jupiter)

0.167 R♃

Mass

4.18 M⊕

Mass (Jupiter)

0.013 M♃

Density

3.46 g/cm³

Surface Gravity

1.18 g (Earth)

Classification

Planet Type

Super-Earth

ESI Score 0.808

HZ Position Inner

Controversial No

Discovery

Year 2017

Method Radial Velocity

Facility La Silla Observatory

Telescope 3.6 m ESO Telescope

Size rank in cohort

Rank by radius

#153of 1176

top 12.9%

This planet

1.88R⊕

Super-Earth median

1.60R⊕

Nearest-size peers

Kepler-137 c 1.88 R⊕ Kepler-291 c 1.88 R⊕ Kepler-1644 b 1.88 R⊕

Metric	Earth	GJ 3138 c	Jupiter
Radius (R⊕)	1.00	1.88	11.21
Mass (M⊕)	1.00	4.18	317.83
Density (g/cm³)	5.51	3.46	1.33
Surface Gravity (g)	1.00	1.18	2.53
Insolation (S⊕)	1.00	13.90	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	4.180 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HIP

HIP 10037

TIC

TIC 632528291

Gaia DR2

Gaia DR2 5144740907820131840

Gaia DR3

Gaia DR3 5144740907820131840

System

GJ 3138

Percentile among Super-Earth cohort

Radius 1.880 R⊕ · percentile 86 / cohort 1176

Mass 4.180 M⊕ · percentile 79 / cohort 1176

Orbital period 5.97 d · percentile 47 / cohort 1164

Distance 28.47 pc · percentile 6 / cohort 1171

ESI 0.808 · percentile 90 / cohort 1176

Orbit & Habitability

Orbital Dynamics

Period

5.974 days

Semi-major axis

0.0570 AU

Eccentricity

0.110

Inclination

— °

Year Length

A year here lasts approximately 5.97 Earth days (1.6% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0570 AU.

Eq. Temperature

—

Insolation (S⊕)

13.90

Earth = 1.00

Earth Similarity (ESI)

0.808

0 = alien, 1 = Earth-identical

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

Discovery Paper

Primary reference

Astudillo Defru et al. 2017

Instrument

HARPS Spectrograph

Publication

2017-06

Observation locale

Ground

Discovery cohort

Planets confirmed in 2017 at La Silla Observatory (12 shown).

GJ 273 c · Rocky Terrestrial Ross 128 b · Rocky Terrestrial GJ 3138 b · Rocky Terrestrial GJ 3323 c · Super-Earth GJ 3323 b · Rocky Terrestrial GJ 273 b · Super-Earth GJ 3293 e · Super-Earth YZ Cet d · Rocky Terrestrial YZ Cet c · Rocky Terrestrial GJ 3293 d · Sub-Neptune YZ Cet b · Rocky Terrestrial GJ 3138 d · Sub-Neptune

Host System: GJ 3138

Spectral Class

M-type red dwarf

Effective Temperature

3,717 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.500 R☉

Stellar Mass

0.681 M☉

Metallicity [Fe/H]

-0.30

Extended Stellar Properties

Surface gravity (log g)

4.629 dex

Stellar density

3.471 g/cm³

Systemic radial velocity

13.60 km/s

Rotation period

42.50 days

Metallicity ratio

[Fe/H]

Distance

28.47 parsec

Light-years 92.86 ly

V-band magnitude

10.83 mag

Voyager-speed travel 1,637,595 yr

Multi-band Host Photometry — 10 bands

Astrometric Data

Parallax

35.094 mas

Total Proper Motion

522.394 mas/yr

PM Right Ascension

516.32 mas/yr

PM Declination

79.40 mas/yr

Galactic Cartesian (pc)

x = 0.811 · y = 0.513 · z = -0.281

Equatorial (J2000)

RA 32.29774° · Dec -16.33925°

Galactic ℓ, b

185.998° · -69.010°

Ecliptic λ, β

23.842° · -27.520°

HTM-20 index

-1157587313