Key parameters at a glance

A radius of 8.29 Earth radii
A mass of 43.40 Earth masses
Surface gravity around 0.63 g
An orbital period of 19.239 days
Semi-major axis 0.1430 AU
Equilibrium temperature 661 K (388 °C)
Distance from Earth 2,049.10 light-years
Earth Similarity Index 0.218
Travel time at Voyager 1 speed 36,135,839 years

2 siblings around Kepler-9

Kepler-9 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-9 d	Super-Earth	1.64	8.41	1.593	2,026	2010
Kepler-9 b this	Neptune-like	8.29	43.40	19.239	661	2010
Kepler-9 c	Neptune-like	8.08	29.90	38.985	523	2010

Kepler-9 b Planet Profile

Physical Specs

Radius

8.29 R⊕

Radius (Jupiter)

0.740 R♃

Mass

43.40 M⊕

Mass (Jupiter)

0.137 M♃

Density

0.42 g/cm³

Surface Gravity

0.63 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.218

HZ Position Inner

Controversial No

Discovery

Year 2010

Method Transit

Facility Kepler

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#138of 574

top 23.9%

This planet

8.29R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

TOI-3629 b 8.29 R⊕ HD 149026 b 8.29 R⊕ DMPP-2 c 8.26 R⊕

Metric	Earth	Kepler-9 b	Jupiter
Radius (R⊕)	1.00	8.29	11.21
Mass (M⊕)	1.00	43.40	317.83
Density (g/cm³)	5.51	0.42	1.33
Surface Gravity (g)	1.00	0.63	2.53
Insolation (S⊕)	1.00	48.23	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	43.400 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	25.904 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

TIC

TIC 120571842

Gaia DR2

Gaia DR2 2099925719951103872

Gaia DR3

Gaia DR3 2099925719951103872

System

Kepler-9

Percentile among Neptune-like cohort

Radius 8.290 R⊕ · percentile 76 / cohort 574

Mass 43.400 M⊕ · percentile 66 / cohort 574

Orbital period 19.24 d · percentile 51 / cohort 524

Distance 628.26 pc · percentile 61 / cohort 572

ESI 0.218 · percentile 31 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

19.239 days

Semi-major axis

0.1430 AU

Eccentricity

0.061

Inclination

88.98 °

Year Length

A year here lasts approximately 19.24 Earth days (5.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1430 AU.

Transit Fingerprint

Depth

0.666 %

Duration

4.243 h

Impact parameter b

0.590

Rp / R★

0.077600

Transit midpoint (BJD)

2,454,977.5120

Photometric dip

Transit produces a flux drop of 6,661 ppm lasting ≈ 4.24 h.

Extended Orbital Architecture

Planet / star radius ratio

0.077600

Semi-major axis / stellar radius

31.300

Impact parameter (b)

0.590

RV semi-amplitude (K)

9.560 m/s

Transit mid-time (BJD)

2,454,977.5120

Long. of periastron (ω)

357.00°

Sky-projected obliquity (λ)

-13.00°

True obliquity (ψ)

28.10°

Angular separation (arcsec)

0.22800

Eq. Temperature

661K

(388 °C)

Insolation (S⊕)

48.23

Earth = 1.00

Earth Similarity (ESI)

0.218

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

Holman et al. 2010

Instrument

Kepler CCD Array

Publication

2010-10

Observation locale

Space

Discovery cohort

Planets confirmed in 2010 at Kepler (11 shown).

Kepler-11 g · Sub-Neptune Kepler-11 f · Sub-Neptune Kepler-11 d · Sub-Neptune Kepler-11 e · Neptune-like Kepler-11 b · Super-Earth Kepler-9 c · Neptune-like Kepler-11 c · Sub-Neptune Kepler-9 d · Super-Earth Kepler-40 b · Gas Giant Kepler-8 b · Gas Giant KOI-217 b · Gas Giant

Host System: Kepler-9

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,774 K — cooler than the Sun (5,778 K)

Estimated Age

2.00 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.958 R☉

Stellar Mass

1.022 M☉

Metallicity [Fe/H]

0.05

Extended Stellar Properties

Surface gravity (log g)

4.490 dex

Stellar density

1.640 g/cm³

Rotational v·sin i

2.74 km/s

Rotation period

16.49 days

Metallicity ratio

[Fe/H]

Distance

628.26 parsec

Light-years 2,049.10 ly

V-band magnitude

13.92 mag

Voyager-speed travel 36,135,839 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

1.563 mas

Total Proper Motion

14.922 mas/yr

PM Right Ascension

2.49 mas/yr

PM Declination

-14.71 mas/yr

Galactic Cartesian (pc)

x = 0.210 · y = -0.755 · z = 0.621

Equatorial (J2000)

RA 285.57399° · Dec 38.40082°

Galactic ℓ, b

68.980° · 14.490°

Ecliptic λ, β

295.275° · 60.481°

HTM-20 index

489015344