Key parameters at a glance

A radius of 1.51 Earth radii
A mass of 2.10 Earth masses
Surface gravity around 0.92 g
An orbital period of 23.092 days
Semi-major axis 0.1288 AU
Equilibrium temperature 345 K (72 °C)
Distance from Earth 218.08 light-years
Earth Similarity Index 0.785
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 d 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	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 this	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 d Planet Profile

Physical Specs

Radius

1.51 R⊕

Radius (Jupiter)

0.135 R♃

Mass

2.10 M⊕

Mass (Jupiter)

0.007 M♃

Density

3.60 g/cm³

Surface Gravity

0.92 g (Earth)

Classification

Planet Type

Super-Earth

ESI Score 0.785

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

#730of 1176

top 62.0%

This planet

1.51R⊕

Super-Earth median

1.60R⊕

Nearest-size peers

Kepler-249 c 1.51 R⊕ Kepler-205 b 1.51 R⊕ Kepler-389 b 1.51 R⊕

Metric	Earth	Kepler-138 d	Jupiter
Radius (R⊕)	1.00	1.51	11.21
Mass (M⊕)	1.00	2.10	317.83
Density (g/cm³)	5.51	3.60	1.33
Surface Gravity (g)	1.00	0.92	2.53
Insolation (S⊕)	1.00	3.40	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	2.100 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 Super-Earth cohort

Radius 1.510 R⊕ · percentile 37 / cohort 1176

Mass 2.100 M⊕ · percentile 2 / cohort 1176

Orbital period 23.09 d · percentile 88 / cohort 1164

Distance 66.86 pc · percentile 13 / cohort 1171

ESI 0.785 · percentile 88 / cohort 1176

Orbit & Habitability

Orbital Dynamics

Period

23.092 days

Semi-major axis

0.1288 AU

Eccentricity

0.010

Inclination

89.04 °

Year Length

A year here lasts approximately 23.09 Earth days (6.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1288 AU.

Transit Fingerprint

Depth

0.060 %

Duration

1.701 h

Impact parameter b

0.870

Rp / R★

0.022578

Transit midpoint (BJD)

2,454,957.8160

Photometric dip

Transit produces a flux drop of 598 ppm lasting ≈ 1.70 h.

Extended Orbital Architecture

Planet / star radius ratio

0.022578

Semi-major axis / stellar radius

51.800

Impact parameter (b)

0.870

Transit mid-time (BJD)

2,454,957.8160

Long. of periastron (ω)

250.00°

Angular separation (arcsec)

1.93000

Eq. Temperature

345K

(72 °C)

Insolation (S⊕)

3.40

Earth = 1.00

Earth Similarity (ESI)

0.785

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — liquid water is physically possible with adequate atmospheric pressure. 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

Kipping 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-333 c · Rocky Terrestrial Kepler-331 d · Super-Earth Kepler-267 d · Sub-Neptune Kepler-220 d · Rocky Terrestrial

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