Key parameters at a glance

A radius of 1.21 Earth radii
A mass of 1.92 Earth masses
Surface gravity around 1.31 g
An orbital period of 2.698 days
Semi-major axis 0.0338 AU
Equilibrium temperature 914 K (641 °C)
Distance from Earth 422.24 light-years
Earth Similarity Index 0.342
Travel time at Voyager 1 speed 7,446,229 years
Almost certainly tidally locked to its host star given the close orbit

K2-228 b Planet Profile

Physical Specs

Radius

1.21 R⊕

Radius (Jupiter)

0.108 R♃

Mass

1.92 M⊕

Mass (Jupiter)

0.006 M♃

Density

5.96 g/cm³

Surface Gravity

1.31 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.342

HZ Position Unknown

Controversial No

Discovery

Year 2018

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#56of 570

top 9.6%

This planet

1.21R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-415 b 1.21 R⊕ Kepler-169 c 1.21 R⊕ Kepler-189 b 1.21 R⊕

Metric	Earth	K2-228 b	Jupiter
Radius (R⊕)	1.00	1.21	11.21
Mass (M⊕)	1.00	1.92	317.83
Density (g/cm³)	5.51	5.96	1.33
Surface Gravity (g)	1.00	1.31	2.53
Insolation (S⊕)	1.00	—	0.037

Star Catalogue Identifiers

TIC

TIC 98751904

Gaia DR2

Gaia DR2 3583611726987567232

Gaia DR3

Gaia DR3 3583611726988838144

System

K2-228

Percentile among Rocky Terrestrial cohort

Radius 1.210 R⊕ · percentile 87 / cohort 570

Mass 1.920 M⊕ · percentile 80 / cohort 570

Orbital period 2.70 d · percentile 30 / cohort 567

Distance 129.46 pc · percentile 26 / cohort 566

ESI 0.342 · percentile 49 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

2.698 days

Semi-major axis

0.0338 AU

Eccentricity

—

Inclination

87.47 °

Year Length

A year here lasts approximately 2.70 Earth days (0.7% of a terrestrial year) at a mean orbital distance of 0.0338 AU.

Transit Fingerprint

Depth

0.026 %

Duration

1.500 h

Impact parameter b

0.420

Rp / R★

0.017000

Transit midpoint (BJD)

2,457,583.1943

Photometric dip

Transit produces a flux drop of 259 ppm lasting ≈ 1.50 h.

Extended Orbital Architecture

Planet / star radius ratio

0.017000

Semi-major axis / stellar radius

12.200

Impact parameter (b)

0.420

Transit mid-time (BJD)

2,457,583.1943

Angular separation (arcsec)

0.26100

Eq. Temperature

914K

(641 °C)

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.342

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

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: K2-228

Spectral Class

K-type orange

Effective Temperature

4,715 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.650 R☉

Stellar Mass

0.710 M☉

Metallicity [Fe/H]

-0.25

Extended Stellar Properties

Surface gravity (log g)

4.660 dex

Stellar density

4.352 g/cm³

Systemic radial velocity

-2.86 km/s

Metallicity ratio

[Fe/H]

Distance

129.46 parsec

Light-years 422.24 ly

V-band magnitude

13.03 mag

Voyager-speed travel 7,446,229 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

7.708 mas

Total Proper Motion

18.795 mas/yr

PM Right Ascension

-12.74 mas/yr

PM Declination

13.82 mas/yr

Galactic Cartesian (pc)

x = -0.985 · y = -0.126 · z = -0.119

Equatorial (J2000)

RA 187.29470° · Dec -6.83420°

Galactic ℓ, b

293.116° · 55.613°

Ecliptic λ, β

189.394° · -3.384°

HTM-20 index

684139555