Key parameters at a glance

A radius of 0.80 Earth radii
A mass of 0.43 Earth masses
Surface gravity around 0.68 g
An orbital period of 38.230 days
Semi-major axis 0.1803 AU
Equilibrium temperature 292 K (19 °C)
Distance from Earth 218.08 light-years
Earth Similarity Index 0.924
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 e 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	Super-Earth	1.51	2.10	23.092	345	2014
Kepler-138 e this	Rocky Terrestrial	0.80	0.43	38.230	292	2022

Kepler-138 e Planet Profile

Physical Specs

Radius

0.80 R⊕

Radius (Jupiter)

0.071 R♃

Mass

0.43 M⊕

Mass (Jupiter)

0.001 M♃

Density

4.67 g/cm³

Surface Gravity

0.68 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.924

HZ Position Inner

Controversial No

Discovery

Year 2022

Method Transit Timing Variations

Facility Multiple Observatories

Telescope Multiple Telescopes

Size rank in cohort

Rank by radius

#486of 570

top 85.1%

This planet

0.80R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-1581 b 0.80 R⊕ Kepler-1076 b 0.80 R⊕ Kepler-1130 b 0.80 R⊕

Metric	Earth	Kepler-138 e	Jupiter
Radius (R⊕)	1.00	0.80	11.21
Mass (M⊕)	1.00	0.43	317.83
Density (g/cm³)	5.51	4.67	1.33
Surface Gravity (g)	1.00	0.68	2.53
Insolation (S⊕)	1.00	1.73	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.430 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 0.797 R⊕ · percentile 15 / cohort 570

Mass 0.430 M⊕ · percentile 12 / cohort 570

Orbital period 38.23 d · percentile 98 / cohort 567

Distance 66.86 pc · percentile 20 / cohort 566

ESI 0.924 · percentile 91 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

38.230 days

Semi-major axis

0.1803 AU

Eccentricity

0.112

Inclination

88.53 °

Year Length

A year here lasts approximately 38.23 Earth days (10.5% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1803 AU.

Extended Orbital Architecture

Semi-major axis / stellar radius

73.000

Impact parameter (b)

1.800

Long. of periastron (ω)

76.00°

Angular separation (arcsec)

2.70000

Eq. Temperature

292K

(19 °C)

Insolation (S⊕)

1.73

Earth = 1.00

Earth Similarity (ESI)

0.924

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.

Discovery Paper

Primary reference

Piaulet et al. 2022

Instrument

Multiple Instruments

Publication

2022-12

Observation locale

Multiple Locales

Discovery cohort

Planets confirmed in 2022 at Multiple Observatories (12 shown).

HD 93351 b · Super-Earth GJ 1002 b · Rocky Terrestrial GJ 2030 b · Sub-Neptune GJ 3929 c · Sub-Neptune HD 217786 c · Sub-Neptune GJ 1002 c · Rocky Terrestrial HD 155918 b · Sub-Neptune HD 213519 b · Sub-Neptune HD 191939 g · Sub-Neptune GJ 514 b · Sub-Neptune HD 12235 b · Sub-Neptune HD 18143 b · 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