Key parameters at a glance

A radius of 5.50 Earth radii
A mass of 36.74 Earth masses
Surface gravity around 1.21 g
An orbital period of 20.861 days
Semi-major axis 0.1600 AU
Equilibrium temperature 781 K (508 °C)
Distance from Earth 5,429.32 light-years
Earth Similarity Index 0.222
Travel time at Voyager 1 speed 95,746,110 years

2 siblings around Kepler-31

Kepler-31 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-31 b this	Neptune-like	5.50	36.74	20.861	781	2011
Kepler-31 c	Neptune-like	5.30	1,493.70	42.632	615	2011
Kepler-31 d	Sub-Neptune	3.90	2,161.24	87.645	484	2014

Kepler-31 b Planet Profile

Physical Specs

Radius

5.50 R⊕

Radius (Jupiter)

0.491 R♃

Mass

36.74 M⊕

Mass (Jupiter)

0.116 M♃

Density

0.78 g/cm³

Surface Gravity

1.21 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.222

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

#317of 574

top 55.1%

This planet

5.50R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

KIC 10525077 b 5.50 R⊕ Kepler-957 b 5.50 R⊕ Kepler-18 c 5.49 R⊕

Metric	Earth	Kepler-31 b	Jupiter
Radius (R⊕)	1.00	5.50	11.21
Mass (M⊕)	1.00	36.74	317.83
Density (g/cm³)	5.51	0.78	1.33
Surface Gravity (g)	1.00	1.21	2.53
Insolation (S⊕)	1.00	91.47	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	36.742 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 270788519

Gaia DR2

Gaia DR2 2128013019361703936

Gaia DR3

Gaia DR3 2128013019361703936

System

Kepler-31

Percentile among Neptune-like cohort

Radius 5.500 R⊕ · percentile 44 / cohort 574

Mass 36.742 M⊕ · percentile 59 / cohort 574

Orbital period 20.86 d · percentile 52 / cohort 524

Distance 1,664.64 pc · percentile 86 / cohort 572

ESI 0.222 · percentile 33 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

20.861 days

Semi-major axis

0.1600 AU

Eccentricity

0.000

Inclination

89.88 °

Year Length

A year here lasts approximately 20.86 Earth days (5.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1600 AU.

Transit Fingerprint

Depth

0.190 %

Duration

4.992 h

Impact parameter b

0.833

Rp / R★

0.041100

Transit midpoint (BJD)

2,454,992.1410

Photometric dip

Transit produces a flux drop of 1,895 ppm lasting ≈ 4.99 h.

Extended Orbital Architecture

Planet / star radius ratio

0.041100

Semi-major axis / stellar radius

31.855

Impact parameter (b)

0.833

Transit mid-time (BJD)

2,454,992.1410

Angular separation (arcsec)

0.09610

Eq. Temperature

781K

(508 °C)

Insolation (S⊕)

91.47

Earth = 1.00

Earth Similarity (ESI)

0.222

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.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Fabrycky et al. 2012

Instrument

Kepler CCD Array

Publication

2012-05

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-31

Spectral Class

F-type yellow-white

Effective Temperature

6,340 K — hotter than the Sun (5,778 K)

Estimated Age

0.28 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

1.220 R☉

Stellar Mass

1.210 M☉

Metallicity [Fe/H]

-0.08

Extended Stellar Properties

Surface gravity (log g)

4.696 dex

Stellar density

0.610 g/cm³

Metallicity ratio

[Fe/H]

Distance

1,664.64 parsec

Light-years 5,429.32 ly

V-band magnitude

15.50 mag

Voyager-speed travel 95,746,110 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

0.572 mas

Total Proper Motion

7.414 mas/yr

PM Right Ascension

-1.02 mas/yr

PM Declination

-7.34 mas/yr

Galactic Cartesian (pc)

x = 0.284 · y = -0.636 · z = 0.718

Equatorial (J2000)

RA 294.02302° · Dec 45.85305°

Galactic ℓ, b

78.627° · 11.957°

Ecliptic λ, β

313.549° · 65.699°

HTM-20 index

-1489710077