Key parameters at a glance

A radius of 1.80 Earth radii
A mass of 3.88 Earth masses
Surface gravity around 1.20 g
An orbital period of 53.647 days
Semi-major axis 0.1960 AU
Equilibrium temperature 216 K (-57 °C)
Distance from Earth 18.20 light-years
Earth Similarity Index 0.698
Travel time at Voyager 1 speed 320,981 years

1 sibling around GJ 251

GJ 251 c shares its host star with 1 other confirmed planet. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
GJ 251 b	Super-Earth	1.79	3.85	14.237	336	2020
GJ 251 c this	Super-Earth	1.80	3.88	53.647	216	2025

GJ 251 c Planet Profile

Physical Specs

Radius

1.80 R⊕

Radius (Jupiter)

0.160 R♃

Mass

3.88 M⊕

Mass (Jupiter)

0.012 M♃

Density

3.66 g/cm³

Surface Gravity

1.20 g (Earth)

Classification

Planet Type

Super-Earth

ESI Score 0.698

HZ Position Habitable

Controversial No

Discovery

Year 2025

Method Radial Velocity

Facility Multiple Observatories

Telescope Multiple Telescopes

Size rank in cohort

Rank by radius

#253of 1176

top 21.4%

This planet

1.80R⊕

Super-Earth median

1.60R⊕

Nearest-size peers

PSR B1257+12 d 1.80 R⊕ Kepler-11 b 1.80 R⊕ Kepler-148 b 1.80 R⊕

Metric	Earth	GJ 251 c	Jupiter
Radius (R⊕)	1.00	1.80	11.21
Mass (M⊕)	1.00	3.88	317.83
Density (g/cm³)	5.51	3.66	1.33
Surface Gravity (g)	1.00	1.20	2.53
Insolation (S⊕)	1.00	0.40	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	3.880 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 265866

HIP

HIP 33226

TIC

TIC 68581262

Gaia DR2

Gaia DR2 939072613334579328

Gaia DR3

Gaia DR3 939072613334579328

System

GJ 251

Percentile among Super-Earth cohort

Radius 1.800 R⊕ · percentile 77 / cohort 1176

Mass 3.880 M⊕ · percentile 70 / cohort 1176

Orbital period 53.65 d · percentile 96 / cohort 1164

Distance 5.58 pc · percentile 0 / cohort 1171

ESI 0.698 · percentile 85 / cohort 1176

Orbit & Habitability

Orbital Dynamics

Period

53.647 days

Semi-major axis

0.1960 AU

Eccentricity

0.000

Inclination

— °

Year Length

A year here lasts approximately 53.65 Earth days (14.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1960 AU.

Extended Orbital Architecture

RV semi-amplitude (K)

1.230 m/s

Transit mid-time (BJD)

2,458,922.0000

Long. of periastron (ω)

0.00°

Angular separation (arcsec)

35.10000

Eq. Temperature

216K

(-57 °C)

Insolation (S⊕)

0.40

Earth = 1.00

Earth Similarity (ESI)

0.698

0 = alien, 1 = Earth-identical

Within the conservative habitable zone — surface water would be frozen.

Discovery Paper

Primary reference

Beard et al. 2025

Instrument

Multiple Instruments

Publication

2025-11

Observation locale

Ground

Discovery cohort

Planets confirmed in 2025 at Multiple Observatories (12 shown).

Gl 725 A b · Super-Earth HD 20794 f · Sub-Neptune GJ 3998 d · Sub-Neptune HD 86728 b · Sub-Neptune TOI-2015 c · Sub-Neptune Kepler-139 f · Neptune-like HD 73344 d · Gas Giant TOI-1472 c · Sub-Neptune TOI-6695 c · Gas Giant AT2021ueyL b · Gas Giant HIP 111909 b · Gas Giant TOI-6041 c · Gas Giant

Host System: GJ 251

Spectral Class

M-type red dwarf

Effective Temperature

3,342 K — cooler than the Sun (5,778 K)

Estimated Age

6.80 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.360 R☉

Stellar Mass

0.350 M☉

Metallicity [Fe/H]

0.07

Extended Stellar Properties

Surface gravity (log g)

4.870 dex

Stellar density

10.053 g/cm³

Systemic radial velocity

22.30 km/s

Rotational v·sin i

2.00 km/s

Rotation period

122.10 days

Metallicity ratio

[Fe/H]

Distance

5.58 parsec

Light-years 18.20 ly

V-band magnitude

9.89 mag

Voyager-speed travel 320,981 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

179.164 mas

Total Proper Motion

828.347 mas/yr

PM Right Ascension

-726.39 mas/yr

PM Declination

-398.13 mas/yr

Galactic Cartesian (pc)

x = -0.198 · y = 0.812 · z = 0.549

Equatorial (J2000)

RA 103.70025° · Dec 33.26646°

Galactic ℓ, b

182.937° · 15.132°

Ecliptic λ, β

101.611° · 10.378°

HTM-20 index

702762585

Observation Record

Photometric series

Stellar spectra

Archive notes