Key parameters at a glance

A radius of 0.87 Earth radii
A mass of 0.59 Earth masses
Surface gravity around 0.78 g
An orbital period of 2.081 days
Distance from Earth 249.50 light-years
Earth Similarity Index 0.943
Travel time at Voyager 1 speed 4,400,016 years
Almost certainly tidally locked to its host star given the close orbit

K2-209 b Planet Profile

Physical Specs

Radius

0.87 R⊕

Radius (Jupiter)

0.077 R♃

Mass

0.59 M⊕

Mass (Jupiter)

0.002 M♃

Density

4.92 g/cm³

Surface Gravity

0.78 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.943

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

#441of 570

top 77.2%

This planet

0.87R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-1890 b 0.87 R⊕ Kepler-1972 c 0.87 R⊕ Kepler-1907 b 0.87 R⊕

Metric	Earth	K2-209 b	Jupiter
Radius (R⊕)	1.00	0.87	11.21
Mass (M⊕)	1.00	0.59	317.83
Density (g/cm³)	5.51	4.92	1.33
Surface Gravity (g)	1.00	0.78	2.53
Insolation (S⊕)	1.00	—	0.037

Star Catalogue Identifiers

TIC

TIC 257436461

Gaia DR2

Gaia DR2 2537467988442521600

Gaia DR3

Gaia DR3 2537467988442521600

System

K2-209

Percentile among Rocky Terrestrial cohort

Radius 0.869 R⊕ · percentile 23 / cohort 570

Mass 0.586 M⊕ · percentile 18 / cohort 570

Orbital period 2.08 d · percentile 23 / cohort 567

Distance 76.50 pc · percentile 21 / cohort 566

ESI 0.943 · percentile 94 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

2.081 days

Semi-major axis

— AU

Eccentricity

—

Inclination

86.23 °

Year Length

A year here lasts approximately 2.08 Earth days (0.6% of a terrestrial year).

Transit Fingerprint

Rp / R★

0.011177

Transit midpoint (BJD)

2,457,394.2331

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.943

0 = alien, 1 = Earth-identical

Insufficient insolation data. 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 K2-210 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 K2-219 c · Super-Earth

Host System: K2-209

Spectral Class

K-type orange

Effective Temperature

4,720 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.712 R☉

Stellar Mass

0.745 M☉

Metallicity [Fe/H]

-0.06

Extended Stellar Properties

Surface gravity (log g)

4.460 dex

Stellar density

2.251 g/cm³

Systemic radial velocity

-26.20 km/s

Metallicity ratio

[Fe/H]

Distance

76.50 parsec

Light-years 249.50 ly

V-band magnitude

11.06 mag

Voyager-speed travel 4,400,016 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

13.044 mas

Total Proper Motion

242.287 mas/yr

PM Right Ascension

-75.31 mas/yr

PM Declination

-230.28 mas/yr

Galactic Cartesian (pc)

x = 0.967 · y = 0.254 · z = 0.024

Equatorial (J2000)

RA 14.69035° · Dec 1.38281°

Galactic ℓ, b

126.762° · -61.434°

Ecliptic λ, β

14.057° · -4.514°

HTM-20 index

1928144554