Key parameters at a glance

A radius of 2.69 Earth radii
A mass of 7.70 Earth masses
Surface gravity around 1.06 g
An orbital period of 6.894 days
Semi-major axis 0.0706 AU
Equilibrium temperature 949 K (676 °C)
Distance from Earth 1,177.13 light-years
Earth Similarity Index 0.257
Travel time at Voyager 1 speed 20,758,737 years

K2-181 b Planet Profile

Physical Specs

Radius

2.69 R⊕

Radius (Jupiter)

0.240 R♃

Mass

7.70 M⊕

Mass (Jupiter)

0.024 M♃

Density

2.17 g/cm³

Surface Gravity

1.06 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.257

HZ Position Inner

Controversial No

Discovery

Year 2018

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#881of 1978

top 44.5%

This planet

2.69R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-1369 b 2.69 R⊕ Kepler-417 c 2.69 R⊕ HD 28109 b 2.69 R⊕

Metric	Earth	K2-181 b	Jupiter
Radius (R⊕)	1.00	2.69	11.21
Mass (M⊕)	1.00	7.70	317.83
Density (g/cm³)	5.51	2.17	1.33
Surface Gravity (g)	1.00	1.06	2.53
Insolation (S⊕)	1.00	192.00	0.037

Star Catalogue Identifiers

TIC

TIC 366528389

Gaia DR2

Gaia DR2 600874445926411264

Gaia DR3

Gaia DR3 600874445926411264

System

K2-181

Percentile among Sub-Neptune cohort

Radius 2.690 R⊕ · percentile 55 / cohort 1978

Mass 7.700 M⊕ · percentile 51 / cohort 1978

Orbital period 6.89 d · percentile 22 / cohort 1946

Distance 360.91 pc · percentile 39 / cohort 1975

ESI 0.257 · percentile 18 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

6.894 days

Semi-major axis

0.0706 AU

Eccentricity

0.400

Inclination

87.40 °

Year Length

A year here lasts approximately 6.89 Earth days (1.9% of a terrestrial year) on a highly eccentric trajectory at a mean orbital distance of 0.0706 AU.

Transit Fingerprint

Depth

0.083 %

Duration

2.520 h

Impact parameter b

0.480

Rp / R★

0.024850

Transit midpoint (BJD)

2,457,143.7948

Photometric dip

Transit produces a flux drop of 828 ppm lasting ≈ 2.52 h.

Extended Orbital Architecture

Planet / star radius ratio

0.024850

Semi-major axis / stellar radius

14.760

Impact parameter (b)

0.480

Transit mid-time (BJD)

2,457,143.7948

Long. of periastron (ω)

20.00°

Angular separation (arcsec)

0.19600

Eq. Temperature

949K

(676 °C)

Insolation (S⊕)

192.00

Earth = 1.00

Earth Similarity (ESI)

0.257

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

Discovery Paper

Primary reference

Mayo et al. 2018

Instrument

Kepler CCD Array

Publication

2018-03

Observation locale

Space

Discovery cohort

Planets confirmed in 2018 at K2 (12 shown).

K2-190 c · Rocky Terrestrial K2-183 b · Rocky Terrestrial K2-209 b · Rocky Terrestrial K2-210 b · Rocky Terrestrial K2-165 b · Super-Earth K2-169 b · Super-Earth K2-148 b · Super-Earth K2-219 b · Super-Earth K2-190 b · Super-Earth K2-200 b · Super-Earth K2-201 b · Super-Earth K2-170 b · Super-Earth

Host System: K2-181

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,528 K — cooler than the Sun (5,778 K)

Estimated Age

5.90 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

1.060 R☉

Stellar Mass

0.960 M☉

Metallicity [Fe/H]

0.18

Extended Stellar Properties

Surface gravity (log g)

4.350 dex

Stellar density

1.280 g/cm³

Systemic radial velocity

-60.38 km/s

Rotational v·sin i

2.10 km/s

Activity index (log R'HK)

-4.914

Metallicity ratio

[Fe/H]

Distance

360.91 parsec

Light-years 1,177.13 ly

V-band magnitude

12.67 mag

Voyager-speed travel 20,758,737 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

2.742 mas

Total Proper Motion

37.338 mas/yr

PM Right Ascension

16.92 mas/yr

PM Declination

-33.29 mas/yr

Galactic Cartesian (pc)

x = -0.598 · y = 0.778 · z = 0.189

Equatorial (J2000)

RA 127.55411° · Dec 10.91014°

Galactic ℓ, b

214.127° · 26.834°

Ecliptic λ, β

127.161° · -7.816°

HTM-20 index

949306127