Key parameters at a glance

A radius of 7.10 Earth radii
A mass of 2.10 Earth masses
Surface gravity around 0.04 g
An orbital period of 45.154 days
Semi-major axis 0.2514 AU
Equilibrium temperature 543 K (270 °C)
Distance from Earth 2,556.51 light-years
Earth Similarity Index 0.138
Travel time at Voyager 1 speed 45,084,084 years

3 siblings around Kepler-51

Kepler-51 b 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-51 b this	Neptune-like	7.10	2.10	45.154	543	2012
Kepler-51 c	Neptune-like	9.00	4.00	85.312	439	2012
Kepler-51 d	Neptune-like	9.70	7.60	130.194	381	2014
Kepler-51 e	Sub-Neptune	2.18	5.40	264.284	—	2024

Kepler-51 b Planet Profile

Physical Specs

Radius

7.10 R⊕

Radius (Jupiter)

0.633 R♃

Mass

2.10 M⊕

Mass (Jupiter)

0.007 M♃

Density

0.03 g/cm³

Surface Gravity

0.04 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.138

HZ Position Inner

Controversial No

Discovery

Year 2012

Method Transit

Facility Kepler

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#195of 574

top 33.8%

This planet

7.10R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

Kepler-111 c 7.08 R⊕ HAT-P-26 b 7.06 R⊕ WASP-166 b 7.06 R⊕

Metric	Earth	Kepler-51 b	Jupiter
Radius (R⊕)	1.00	7.10	11.21
Mass (M⊕)	1.00	2.10	317.83
Density (g/cm³)	5.51	0.03	1.33
Surface Gravity (g)	1.00	0.04	2.53
Insolation (S⊕)	1.00	10.12	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	2.100 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 27846348

Gaia DR2

Gaia DR2 2135275362382289280

Gaia DR3

Gaia DR3 2135275362382289280

System

Kepler-51

Percentile among Neptune-like cohort

Radius 7.100 R⊕ · percentile 66 / cohort 574

Mass 2.100 M⊕ · percentile 0 / cohort 574

Orbital period 45.15 d · percentile 68 / cohort 524

Distance 783.83 pc · percentile 66 / cohort 572

ESI 0.138 · percentile 10 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

45.154 days

Semi-major axis

0.2514 AU

Eccentricity

0.040

Inclination

89.78 °

Year Length

A year here lasts approximately 45.15 Earth days (12.4% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.2514 AU.

Transit Fingerprint

Depth

0.621 %

Duration

5.797 h

Impact parameter b

0.251

Rp / R★

0.074140

Transit midpoint (BJD)

2,455,714.5977

Photometric dip

Transit produces a flux drop of 6,209 ppm lasting ≈ 5.80 h.

Extended Orbital Architecture

Planet / star radius ratio

0.074140

Semi-major axis / stellar radius

61.500

Impact parameter (b)

0.251

Transit mid-time (BJD)

2,455,714.5977

Long. of periastron (ω)

53.30°

Angular separation (arcsec)

0.32100

Eq. Temperature

543K

(270 °C)

Insolation (S⊕)

10.12

Earth = 1.00

Earth Similarity (ESI)

0.138

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

Steffen et al. 2013

Instrument

Kepler CCD Array

Publication

2013-01

Observation locale

Space

Discovery cohort

Planets confirmed in 2012 at Kepler (12 shown).

Kepler-54 c · Rocky Terrestrial Kepler-49 c · Sub-Neptune Kepler-55 b · Sub-Neptune Kepler-49 b · Sub-Neptune Kepler-81 c · Sub-Neptune Kepler-55 c · Sub-Neptune Kepler-52 c · Super-Earth Kepler-83 c · Sub-Neptune Kepler-32 d · Sub-Neptune Kepler-83 b · Sub-Neptune Kepler-54 b · Sub-Neptune Kepler-80 c · Sub-Neptune

Host System: Kepler-51

Spectral Class

F-type yellow-white

Effective Temperature

6,018 K — hotter than the Sun (5,778 K)

Estimated Age

0.30 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.940 R☉

Stellar Mass

1.040 M☉

Metallicity [Fe/H]

0.05

Extended Stellar Properties

Surface gravity (log g)

4.510 dex

Stellar density

2.160 g/cm³

Rotation period

8.22 days

Metallicity ratio

[M/H]

Distance

783.83 parsec

Light-years 2,556.51 ly

V-band magnitude

14.89 mag

Voyager-speed travel 45,084,084 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

1.247 mas

Total Proper Motion

7.458 mas/yr

PM Right Ascension

0.01 mas/yr

PM Declination

-7.46 mas/yr

Galactic Cartesian (pc)

x = 0.287 · y = -0.576 · z = 0.765

Equatorial (J2000)

RA 296.47976° · Dec 49.93765°

Galactic ℓ, b

83.113° · 12.362°

Ecliptic λ, β

322.007° · 68.646°

HTM-20 index

-464884401