Key parameters at a glance

A radius of 1.86 Earth radii
A mass of 2.06 Earth masses
Surface gravity around 0.60 g
An orbital period of 8.990 days
Semi-major axis 0.0752 AU
Equilibrium temperature 509 K (236 °C)
Distance from Earth 1,429.73 light-years
Earth Similarity Index 0.496
Travel time at Voyager 1 speed 25,213,361 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

Kepler-28 is an M-type main-sequence star about 1,450 light-years away in the northern constellation of Cygnus. With an apparent visual magnitude of 15.036, this star is too faint to be seen with the naked eye. It is orbited by two exoplanets.

Excerpted from Wikipedia · full article

1 sibling around Kepler-28

Kepler-28 c shares its host star with 1 other confirmed planet. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
Kepler-28 b	Super-Earth	1.96	1.63	5.910	585	2011
Kepler-28 c this	Super-Earth	1.86	2.06	8.990	509	2011

Kepler-28 c Planet Profile

Physical Specs

Radius

1.86 R⊕

Radius (Jupiter)

0.166 R♃

Mass

2.06 M⊕

Mass (Jupiter)

0.006 M♃

Density

1.76 g/cm³

Surface Gravity

0.60 g (Earth)

Classification

Planet Type

Super-Earth

ESI Score 0.496

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

#187of 1176

top 15.8%

This planet

1.86R⊕

Super-Earth median

1.60R⊕

Nearest-size peers

Kepler-1827 b 1.86 R⊕ Kepler-191 c 1.86 R⊕ Kepler-299 d 1.86 R⊕

Metric	Earth	Kepler-28 c	Jupiter
Radius (R⊕)	1.00	1.86	11.21
Mass (M⊕)	1.00	2.06	317.83
Density (g/cm³)	5.51	1.76	1.33
Surface Gravity (g)	1.00	0.60	2.53
Insolation (S⊕)	1.00	35.90	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	2.060 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 63122956

Gaia DR2

Gaia DR2 2125731464014361088

Gaia DR3

Gaia DR3 2125731464014361088

System

Kepler-28

Percentile among Super-Earth cohort

Radius 1.857 R⊕ · percentile 84 / cohort 1176

Mass 2.060 M⊕ · percentile 1 / cohort 1176

Orbital period 8.99 d · percentile 62 / cohort 1164

Distance 438.36 pc · percentile 43 / cohort 1171

ESI 0.496 · percentile 72 / cohort 1176

Orbit & Habitability

Orbital Dynamics

Period

8.990 days

Semi-major axis

0.0752 AU

Eccentricity

0.017

Inclination

89.98 °

Year Length

A year here lasts approximately 8.99 Earth days (2.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0752 AU.

Transit Fingerprint

Depth

0.091 %

Duration

2.861 h

Impact parameter b

0.008

Rp / R★

0.026527

Transit midpoint (BJD)

2,455,008.6842

Photometric dip

Transit produces a flux drop of 905 ppm lasting ≈ 2.86 h.

Extended Orbital Architecture

Planet / star radius ratio

0.026527

Semi-major axis / stellar radius

24.640

Impact parameter (b)

0.008

Transit mid-time (BJD)

2,455,008.6842

Angular separation (arcsec)

0.17200

Eq. Temperature

509K

(236 °C)

Insolation (S⊕)

35.90

Earth = 1.00

Earth Similarity (ESI)

0.496

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

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. 2012

Instrument

Kepler CCD Array

Publication

2012-04

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-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 Kepler-29 c · Sub-Neptune

Host System: Kepler-28

Spectral Class

M-type red dwarf

Effective Temperature

4,499 K — cooler than the Sun (5,778 K)

Estimated Age

1.91 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.664 R☉

Stellar Mass

0.684 M☉

Metallicity [Fe/H]

0.15

Extended Stellar Properties

Surface gravity (log g)

4.620 dex

Stellar density

3.271 g/cm³

Metallicity ratio

[M/H]

Distance

438.36 parsec

Light-years 1,429.73 ly

V-band magnitude

15.13 mag

Voyager-speed travel 25,213,361 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

2.253 mas

Total Proper Motion

11.702 mas/yr

PM Right Ascension

-0.49 mas/yr

PM Declination

11.69 mas/yr

Galactic Cartesian (pc)

x = 0.278 · y = -0.684 · z = 0.675

Equatorial (J2000)

RA 292.13704° · Dec 42.42948°

Galactic ℓ, b

74.881° · 11.639°

Ecliptic λ, β

307.770° · 62.995°

HTM-20 index

-242081587

Wikipedia → Image: Wikimedia Commons · Marhorr · CC BY-SA 3.0