Key parameters at a glance

A radius of 1.18 Earth radii
A mass of 1.78 Earth masses
Surface gravity around 1.28 g
An orbital period of 1.220 days
Semi-major axis 0.0197 AU
Distance from Earth 92.86 light-years
Earth Similarity Index 0.946
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 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
GJ 3138 b this	Rocky Terrestrial	1.18	1.78	1.220	—	2017
GJ 3138 c	Super-Earth	1.88	4.18	5.974	—	2017
GJ 3138 d	Sub-Neptune	3.23	10.50	257.800	—	2017

GJ 3138 b Planet Profile

Physical Specs

Radius

1.18 R⊕

Radius (Jupiter)

0.106 R♃

Mass

1.78 M⊕

Mass (Jupiter)

0.006 M♃

Density

5.95 g/cm³

Surface Gravity

1.28 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.946

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

#117of 570

top 20.4%

This planet

1.18R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-1430 b 1.18 R⊕ Kepler-1512 b 1.18 R⊕ Kepler-332 d 1.18 R⊕

Metric	Earth	GJ 3138 b	Jupiter
Radius (R⊕)	1.00	1.18	11.21
Mass (M⊕)	1.00	1.78	317.83
Density (g/cm³)	5.51	5.95	1.33
Surface Gravity (g)	1.00	1.28	2.53
Insolation (S⊕)	1.00	118.10	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	1.780 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 Rocky Terrestrial cohort

Radius 1.180 R⊕ · percentile 77 / cohort 570

Mass 1.780 M⊕ · percentile 73 / cohort 570

Orbital period 1.22 d · percentile 13 / cohort 567

Distance 28.47 pc · percentile 13 / cohort 566

ESI 0.946 · percentile 94 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

1.220 days

Semi-major axis

0.0197 AU

Eccentricity

0.190

Inclination

— °

Year Length

A year here lasts approximately 1.22 Earth days (0.3% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0197 AU.

Eq. Temperature

—

Insolation (S⊕)

118.10

Earth = 1.00

Earth Similarity (ESI)

0.946

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