Key parameters at a glance

A radius of 2.57 Earth radii
A mass of 7.14 Earth masses
Surface gravity around 1.08 g
An orbital period of 6.905 days
Semi-major axis 0.0608 AU
Equilibrium temperature 590 K (317 °C)
Distance from Earth 55.21 light-years
Earth Similarity Index 0.422
Travel time at Voyager 1 speed 973,698 years
Almost certainly tidally locked to its host star given the close orbit

GJ 3942 b Planet Profile

Physical Specs

Radius

2.57 R⊕

Radius (Jupiter)

0.229 R♃

Mass

7.14 M⊕

Mass (Jupiter)

0.022 M♃

Density

2.31 g/cm³

Surface Gravity

1.08 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.422

HZ Position Unknown

Controversial No

Discovery

Year 2017

Method Radial Velocity

Facility Roque de los Muchachos Observatory

Telescope 3.58 m Telescopio Nazionale Galileo

Size rank in cohort

Rank by radius

#1074of 1978

top 54.2%

This planet

2.57R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-1549 b 2.57 R⊕ Kepler-245 b 2.57 R⊕ Kepler-313 c 2.57 R⊕

Metric	Earth	GJ 3942 b	Jupiter
Radius (R⊕)	1.00	2.57	11.21
Mass (M⊕)	1.00	7.14	317.83
Density (g/cm³)	5.51	2.31	1.33
Surface Gravity (g)	1.00	1.08	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	7.140 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HIP

HIP 79126

TIC

TIC 162494287

Gaia DR2

Gaia DR2 1428030622526979968

Gaia DR3

Gaia DR3 1428030622526979968

System

GJ 3942

Percentile among Sub-Neptune cohort

Radius 2.570 R⊕ · percentile 45 / cohort 1978

Mass 7.140 M⊕ · percentile 42 / cohort 1978

Orbital period 6.91 d · percentile 22 / cohort 1946

Distance 16.93 pc · percentile 3 / cohort 1975

ESI 0.422 · percentile 57 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

6.905 days

Semi-major axis

0.0608 AU

Eccentricity

0.121

Inclination

— °

Year Length

A year here lasts approximately 6.91 Earth days (1.9% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0608 AU.

Eq. Temperature

590K

(317 °C)

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.422

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

Perger et al. 2017

Instrument

HARPS-N Spectrograph

Publication

2017-12

Observation locale

Ground

Discovery cohort

Planets confirmed in 2017 at Roque de los Muchachos Observatory (2 shown).

Kepler-19 d · Neptune-like TYC 4282-00605-1 b · Gas Giant

Host System: GJ 3942

Spectral Class

M-type red dwarf

Effective Temperature

3,867 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.610 R☉

Stellar Mass

0.630 M☉

Metallicity [Fe/H]

-0.04

Extended Stellar Properties

Surface gravity (log g)

4.650 dex

Stellar density

4.167 g/cm³

Systemic radial velocity

-19.37 km/s

Rotational v·sin i

1.67 km/s

Metallicity ratio

[Fe/H]

Distance

16.93 parsec

Light-years 55.21 ly

V-band magnitude

10.17 mag

Voyager-speed travel 973,698 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

59.042 mas

Total Proper Motion

213.147 mas/yr

PM Right Ascension

203.93 mas/yr

PM Declination

61.99 mas/yr

Galactic Cartesian (pc)

x = -0.280 · y = -0.533 · z = 0.798

Equatorial (J2000)

RA 242.26455° · Dec 52.94414°

Galactic ℓ, b

82.205° · 45.469°

Ecliptic λ, β

211.503° · 70.796°

HTM-20 index

1869311375