Key parameters at a glance

A radius of 2.00 Earth radii
A mass of 6.90 Earth masses
Surface gravity around 1.73 g
An orbital period of 3.505 days
Semi-major axis 0.0447 AU
Equilibrium temperature 1,165 K (892 °C)
Distance from Earth 1,412.41 light-years
Earth Similarity Index 0.240
Travel time at Voyager 1 speed 24,907,827 years

2 siblings around Kepler-18

Kepler-18 b shares its host star with 2 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
Kepler-18 b this	Sub-Neptune	2.00	6.90	3.505	1,165	2011
Kepler-18 c	Neptune-like	5.49	17.30	7.642	899	2011
Kepler-18 d	Neptune-like	6.98	16.40	14.859	720	2011

Kepler-18 b Planet Profile

Physical Specs

Radius

2.00 R⊕

Radius (Jupiter)

0.178 R♃

Mass

6.90 M⊕

Mass (Jupiter)

0.022 M♃

Density

4.90 g/cm³

Surface Gravity

1.73 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.240

HZ Position Inner

Controversial No

Discovery

Year 2011

Method Transit

Facility Kepler

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1955of 1978

top 98.8%

This planet

2.00R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-238 f 2.00 R⊕ Kepler-242 c 2.00 R⊕ Kepler-179 c 2.00 R⊕

Metric	Earth	Kepler-18 b	Jupiter
Radius (R⊕)	1.00	2.00	11.21
Mass (M⊕)	1.00	6.90	317.83
Density (g/cm³)	5.51	4.90	1.33
Surface Gravity (g)	1.00	1.73	2.53
Insolation (S⊕)	1.00	355.74	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	6.900 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	12.751 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

TIC

TIC 273690178

Gaia DR2

Gaia DR2 2079295583282164992

Gaia DR3

Gaia DR3 2079295583282164992

System

Kepler-18

Percentile among Sub-Neptune cohort

Radius 2.000 R⊕ · percentile 0 / cohort 1978

Mass 6.900 M⊕ · percentile 39 / cohort 1978

Orbital period 3.50 d · percentile 7 / cohort 1946

Distance 433.05 pc · percentile 43 / cohort 1975

ESI 0.240 · percentile 14 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

3.505 days

Semi-major axis

0.0447 AU

Eccentricity

0.000

Inclination

84.92 °

Year Length

A year here lasts approximately 3.50 Earth days (1.0% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0447 AU.

Transit Fingerprint

Depth

0.025 %

Duration

2.076 h

Impact parameter b

0.771

Rp / R★

0.016560

Transit midpoint (BJD)

2,454,966.5068

Photometric dip

Transit produces a flux drop of 254 ppm lasting ≈ 2.08 h.

Extended Orbital Architecture

Planet / star radius ratio

0.016560

Semi-major axis / stellar radius

8.580

Impact parameter (b)

0.771

RV semi-amplitude (K)

5.200 m/s

Transit mid-time (BJD)

2,454,966.5068

Angular separation (arcsec)

0.10300

Eq. Temperature

1,165K

(892 °C)

Insolation (S⊕)

355.74

Earth = 1.00

Earth Similarity (ESI)

0.240

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched.

Detection Signatures

Transit photometry

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

Radial velocity

Stellar wobble has been measured spectroscopically.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Cochran et al. 2011

Instrument

Kepler CCD Array

Publication

2011-11

Observation locale

Space

Discovery cohort

Planets confirmed in 2011 at Kepler (12 shown).

Kepler-22 b · Sub-Neptune Kepler-20 d · Sub-Neptune Kepler-26 c · Sub-Neptune Kepler-19 c · Sub-Neptune Kepler-26 b · Sub-Neptune Kepler-28 c · Super-Earth Kepler-10 c · Sub-Neptune Kepler-20 f · Rocky Terrestrial Kepler-42 d · Rocky Terrestrial Kepler-16 b · Neptune-like Kepler-28 b · Super-Earth Kepler-34 b · Neptune-like

Host System: Kepler-18

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,345 K — cooler than the Sun (5,778 K)

Estimated Age

10.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

1.108 R☉

Stellar Mass

0.972 M☉

Metallicity [Fe/H]

0.19

Extended Stellar Properties

Surface gravity (log g)

4.310 dex

Stellar density

1.010 g/cm³

Rotational v·sin i

4.00 km/s

Metallicity ratio

[Fe/H]

Distance

433.05 parsec

Light-years 1,412.41 ly

V-band magnitude

13.77 mag

Voyager-speed travel 24,907,827 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

2.280 mas

Total Proper Motion

20.364 mas/yr

PM Right Ascension

-1.43 mas/yr

PM Declination

-20.31 mas/yr

Galactic Cartesian (pc)

x = 0.334 · y = -0.627 · z = 0.704

Equatorial (J2000)

RA 298.07944° · Dec 44.74625°

Galactic ℓ, b

79.007° · 8.920°

Ecliptic λ, β

318.579° · 63.526°

HTM-20 index

1283112230