Key parameters at a glance

A radius of 5.49 Earth radii
A mass of 17.30 Earth masses
Surface gravity around 0.57 g
An orbital period of 7.642 days
Semi-major axis 0.0752 AU
Equilibrium temperature 899 K (626 °C)
Distance from Earth 1,412.41 light-years
Earth Similarity Index 0.188
Travel time at Voyager 1 speed 24,907,827 years

2 siblings around Kepler-18

Kepler-18 c 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	Sub-Neptune	2.00	6.90	3.505	1,165	2011
Kepler-18 c this	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 c Planet Profile

Physical Specs

Radius

5.49 R⊕

Radius (Jupiter)

0.490 R♃

Mass

17.30 M⊕

Mass (Jupiter)

0.054 M♃

Density

0.59 g/cm³

Surface Gravity

0.57 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.188

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

#320of 574

top 55.6%

This planet

5.49R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

KIC 10525077 b 5.50 R⊕ Kepler-31 b 5.50 R⊕ Kepler-957 b 5.50 R⊕

Metric	Earth	Kepler-18 c	Jupiter
Radius (R⊕)	1.00	5.49	11.21
Mass (M⊕)	1.00	17.30	317.83
Density (g/cm³)	5.51	0.59	1.33
Surface Gravity (g)	1.00	0.57	2.53
Insolation (S⊕)	1.00	126.08	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	17.300 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	19.742 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 Neptune-like cohort

Radius 5.490 R⊕ · percentile 44 / cohort 574

Mass 17.300 M⊕ · percentile 19 / cohort 574

Orbital period 7.64 d · percentile 29 / cohort 524

Distance 433.05 pc · percentile 54 / cohort 572

ESI 0.188 · percentile 25 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

7.642 days

Semi-major axis

0.0752 AU

Eccentricity

0.000

Inclination

87.68 °

Year Length

A year here lasts approximately 7.64 Earth days (2.1% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0752 AU.

Transit Fingerprint

Depth

0.229 %

Duration

3.487 h

Impact parameter b

0.593

Rp / R★

0.045490

Transit midpoint (BJD)

2,455,167.0883

Photometric dip

Transit produces a flux drop of 2,287 ppm lasting ≈ 3.49 h.

Extended Orbital Architecture

Planet / star radius ratio

0.045490

Semi-major axis / stellar radius

14.430

Impact parameter (b)

0.593

RV semi-amplitude (K)

5.100 m/s

Transit mid-time (BJD)

2,455,167.0883

Angular separation (arcsec)

0.17400

Eq. Temperature

899K

(626 °C)

Insolation (S⊕)

126.08

Earth = 1.00

Earth Similarity (ESI)

0.188

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

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