Key parameters at a glance

A radius of 2.18 Earth radii
A mass of 5.39 Earth masses
Surface gravity around 1.13 g
An orbital period of 21.750 days
Semi-major axis 0.1210 AU
Distance from Earth 404.94 light-years
Earth Similarity Index 0.754
Travel time at Voyager 1 speed 7,141,156 years
Almost certainly tidally locked to its host star given the close orbit

K2-125 b Planet Profile

Physical Specs

Radius

2.18 R⊕

Radius (Jupiter)

0.194 R♃

Mass

5.39 M⊕

Mass (Jupiter)

0.017 M♃

Density

2.86 g/cm³

Surface Gravity

1.13 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.754

HZ Position Inner

Controversial No

Discovery

Year 2017

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1703of 1978

top 86.0%

This planet

2.18R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

GJ 3090 b 2.18 R⊕ Kepler-261 b 2.18 R⊕ Kepler-250 d 2.18 R⊕

Metric	Earth	K2-125 b	Jupiter
Radius (R⊕)	1.00	2.18	11.21
Mass (M⊕)	1.00	5.39	317.83
Density (g/cm³)	5.51	2.86	1.33
Surface Gravity (g)	1.00	1.13	2.53
Insolation (S⊕)	1.00	2.00	0.037

Star Catalogue Identifiers

TIC

TIC 405673618

Gaia DR2

Gaia DR2 3606324613561098368

Gaia DR3

Gaia DR3 3606324613561098368

System

K2-125

Percentile among Sub-Neptune cohort

Radius 2.180 R⊕ · percentile 13 / cohort 1978

Mass 5.390 M⊕ · percentile 14 / cohort 1978

Orbital period 21.75 d · percentile 65 / cohort 1946

Distance 124.16 pc · percentile 24 / cohort 1975

ESI 0.754 · percentile 97 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

21.750 days

Semi-major axis

0.1210 AU

Eccentricity

0.080

Inclination

89.72 °

Year Length

A year here lasts approximately 21.75 Earth days (6.0% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1210 AU.

Transit Fingerprint

Rp / R★

0.049811

Transit midpoint (BJD)

2,457,243.0880

Extended Orbital Architecture

Planet / star radius ratio

0.049811

Semi-major axis / stellar radius

63.310

Transit mid-time (BJD)

2,457,243.0880

Long. of periastron (ω)

-3.74°

Angular separation (arcsec)

0.97500

Eq. Temperature

—

Insolation (S⊕)

2.00

Earth = 1.00

Earth Similarity (ESI)

0.754

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

Dressing et al. 2017

Instrument

Kepler CCD Array

Publication

2017-11

Observation locale

Space

Discovery cohort

Planets confirmed in 2017 at K2 (12 shown).

K2-129 b · Rocky Terrestrial K2-130 b · Super-Earth K2-133 b · Super-Earth K2-128 b · Super-Earth K2-133 c · Super-Earth K2-116 b · Rocky Terrestrial K2-118 b · Sub-Neptune K2-136 d · Super-Earth K2-123 b · Sub-Neptune K2-136 c · Sub-Neptune K2-124 b · Sub-Neptune K2-117 c · Sub-Neptune

Host System: K2-125

Spectral Class

M-type red dwarf

Effective Temperature

3,654 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.402 R☉

Stellar Mass

0.495 M☉

Metallicity [Fe/H]

—

Distance

124.16 parsec

Light-years 404.94 ly

V-band magnitude

16.40 mag

Voyager-speed travel 7,141,156 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

8.026 mas

Total Proper Motion

72.574 mas/yr

PM Right Ascension

-53.03 mas/yr

PM Declination

-49.54 mas/yr

Galactic Cartesian (pc)

x = -0.882 · y = -0.395 · z = -0.258

Equatorial (J2000)

RA 204.14188° · Dec -14.94782°

Galactic ℓ, b

318.877° · 46.522°

Ecliptic λ, β

207.812° · -4.558°

HTM-20 index

757552284