Key parameters at a glance

A radius of 0.64 Earth radii
A mass of 0.07 Earth masses
Surface gravity around 0.17 g
An orbital period of 10.313 days
Semi-major axis 0.0753 AU
Equilibrium temperature 452 K (179 °C)
Distance from Earth 218.08 light-years
Earth Similarity Index 0.493
Travel time at Voyager 1 speed 3,845,765 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

Kepler-138, also known as KOI-314, is a red dwarf located in the constellation Lyra, 219 light years from Earth. It is located within the field of vision of the Kepler spacecraft, the satellite that NASA's Kepler Mission used to detect planets transiting their stars.

Excerpted from Wikipedia · full article

3 siblings around Kepler-138

Kepler-138 b shares its host star with 3 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
Kepler-138 b this	Rocky Terrestrial	0.64	0.07	10.313	452	2014
Kepler-138 c	Super-Earth	1.51	2.30	13.782	410	2014
Kepler-138 d	Super-Earth	1.51	2.10	23.092	345	2014
Kepler-138 e	Rocky Terrestrial	0.80	0.43	38.230	292	2022

Kepler-138 b Planet Profile

Physical Specs

Radius

0.64 R⊕

Radius (Jupiter)

0.057 R♃

Mass

0.07 M⊕

Mass (Jupiter)

0.000 M♃

Density

1.70 g/cm³

Surface Gravity

0.17 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.493

HZ Position Inner

Controversial No

Discovery

Year 2014

Method Transit

Facility Kepler

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#542of 570

top 94.9%

This planet

0.64R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

K2-137 b 0.64 R⊕ Kepler-1371 c 0.64 R⊕ Barnard e 0.64 R⊕

Metric	Earth	Kepler-138 b	Jupiter
Radius (R⊕)	1.00	0.64	11.21
Mass (M⊕)	1.00	0.07	317.83
Density (g/cm³)	5.51	1.70	1.33
Surface Gravity (g)	1.00	0.17	2.53
Insolation (S⊕)	1.00	9.90	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.070 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 159376971

Gaia DR2

Gaia DR2 2102053446751282944

Gaia DR3

Gaia DR3 2102053446751282944

System

Kepler-138

Percentile among Rocky Terrestrial cohort

Radius 0.640 R⊕ · percentile 5 / cohort 570

Mass 0.070 M⊕ · percentile 1 / cohort 570

Orbital period 10.31 d · percentile 78 / cohort 567

Distance 66.86 pc · percentile 20 / cohort 566

ESI 0.493 · percentile 70 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

10.313 days

Semi-major axis

0.0753 AU

Eccentricity

0.020

Inclination

88.67 °

Year Length

A year here lasts approximately 10.31 Earth days (2.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0753 AU.

Transit Fingerprint

Depth

0.014 %

Duration

1.920 h

Impact parameter b

0.700

Rp / R★

0.010800

Transit midpoint (BJD)

2,454,956.2360

Photometric dip

Transit produces a flux drop of 137 ppm lasting ≈ 1.92 h.

Extended Orbital Architecture

Planet / star radius ratio

0.010800

Semi-major axis / stellar radius

30.300

Impact parameter (b)

0.700

Transit mid-time (BJD)

2,454,956.2360

Long. of periastron (ω)

40.00°

Angular separation (arcsec)

1.13000

Eq. Temperature

452K

(179 °C)

Insolation (S⊕)

9.90

Earth = 1.00

Earth Similarity (ESI)

0.493

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Rowe et al. 2014

Instrument

Kepler CCD Array

Publication

2014-03

Observation locale

Space

Discovery cohort

Planets confirmed in 2014 at Kepler (12 shown).

Kepler-186 e · Super-Earth Kepler-395 c · Super-Earth Kepler-220 e · Super-Earth Kepler-249 d · Super-Earth Kepler-296 f · Super-Earth Kepler-367 c · Rocky Terrestrial Kepler-296 e · Super-Earth Kepler-155 c · Sub-Neptune Kepler-138 d · Super-Earth Kepler-333 c · Rocky Terrestrial Kepler-331 d · Super-Earth Kepler-267 d · Sub-Neptune

Host System: Kepler-138

Spectral Class

M-type red dwarf

Effective Temperature

3,841 K — cooler than the Sun (5,778 K)

Estimated Age

2.21 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.535 R☉

Stellar Mass

0.535 M☉

Metallicity [Fe/H]

-0.18

Extended Stellar Properties

Surface gravity (log g)

4.710 dex

Stellar density

4.900 g/cm³

Systemic radial velocity

-36.33 km/s

Metallicity ratio

[Fe/H]

Distance

66.86 parsec

Light-years 218.08 ly

V-band magnitude

13.04 mag

Voyager-speed travel 3,845,765 yr

Multi-band Host Photometry — 15 bands

Astrometric Data

Parallax

14.927 mas

Total Proper Motion

30.652 mas/yr

PM Right Ascension

-20.60 mas/yr

PM Declination

22.70 mas/yr

Galactic Cartesian (pc)

x = 0.253 · y = -0.682 · z = 0.686

Equatorial (J2000)

RA 290.38141° · Dec 43.29306°

Galactic ℓ, b

75.107° · 13.172°

Ecliptic λ, β

305.661° · 64.230°

HTM-20 index

1052695179

Wikipedia → Image: Wikimedia Commons · ILLUSTRATION: NASA, ESA, Leah Hustak (STScI) · CC BY 4.0