Key parameters at a glance

A radius of 0.78 Earth radii
A mass of 0.71 Earth masses
Surface gravity around 1.16 g
An orbital period of 1.214 days
Semi-major axis 0.0116 AU
Equilibrium temperature 519 K (246 °C)
Distance from Earth 130.66 light-years
Earth Similarity Index 0.278
Travel time at Voyager 1 speed 2,304,127 years
Almost certainly tidally locked to its host star given the close orbit

2 siblings around Kepler-42

Kepler-42 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-42 c	Rocky Terrestrial	0.73	60.34	0.453	720	2011
Kepler-42 b this	Rocky Terrestrial	0.78	0.71	1.214	519	2011
Kepler-42 d	Rocky Terrestrial	0.57	0.36	1.865	450	2011

Kepler-42 b Planet Profile

Physical Specs

Radius

0.78 R⊕

Radius (Jupiter)

0.070 R♃

Mass

0.71 M⊕

Mass (Jupiter)

0.002 M♃

Density

0.15 g/cm³

Surface Gravity

1.16 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.278

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

#493of 570

top 86.3%

This planet

0.78R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-783 b 0.78 R⊕ Kepler-653 c 0.78 R⊕ TRAPPIST-1 d 0.79 R⊕

Metric	Earth	Kepler-42 b	Jupiter
Radius (R⊕)	1.00	0.78	11.21
Mass (M⊕)	1.00	0.71	317.83
Density (g/cm³)	5.51	0.15	1.33
Surface Gravity (g)	1.00	1.16	2.53
Insolation (S⊕)	1.00	22.39	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.706 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 63126862

Gaia DR2

Gaia DR2 2126556132093765888

Gaia DR3

Gaia DR3 2126556132093765888

System

Kepler-42

Percentile among Rocky Terrestrial cohort

Radius 0.780 R⊕ · percentile 13 / cohort 570

Mass 0.706 M⊕ · percentile 25 / cohort 570

Orbital period 1.21 d · percentile 13 / cohort 567

Distance 40.06 pc · percentile 17 / cohort 566

ESI 0.278 · percentile 31 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

1.214 days

Semi-major axis

0.0116 AU

Eccentricity

0.040

Inclination

85.57 °

Year Length

A year here lasts approximately 1.21 Earth days (0.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0116 AU.

Transit Fingerprint

Depth

0.182 %

Duration

0.553 h

Impact parameter b

0.711

Rp / R★

0.041900

Transit midpoint (BJD)

2,455,003.4833

Photometric dip

Transit produces a flux drop of 1,821 ppm lasting ≈ 0.55 h.

Extended Orbital Architecture

Planet / star radius ratio

0.041900

Semi-major axis / stellar radius

12.100

Impact parameter (b)

0.711

Transit mid-time (BJD)

2,455,003.4833

Angular separation (arcsec)

0.29000

Eq. Temperature

519K

(246 °C)

Insolation (S⊕)

22.39

Earth = 1.00

Earth Similarity (ESI)

0.278

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.

Discovery Paper

Primary reference

Muirhead et al. 2012

Instrument

Kepler CCD Array

Publication

2012-03

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-42

Spectral Class

M-type red dwarf

Effective Temperature

3,068 K — cooler than the Sun (5,778 K)

Estimated Age

4.50 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.170 R☉

Stellar Mass

0.130 M☉

Metallicity [Fe/H]

-0.33

Extended Stellar Properties

Surface gravity (log g)

5.110 dex

Stellar density

26.800 g/cm³

Systemic radial velocity

-84.48 km/s

Rotational v·sin i

3.30 km/s

Metallicity ratio

[M/H]

Distance

40.06 parsec

Light-years 130.66 ly

V-band magnitude

16.70 mag

Voyager-speed travel 2,304,127 yr

Multi-band Host Photometry — 15 bands

Astrometric Data

Parallax

24.934 mas

Total Proper Motion

427.682 mas/yr

PM Right Ascension

93.13 mas/yr

PM Declination

-417.42 mas/yr

Galactic Cartesian (pc)

x = 0.269 · y = -0.659 · z = 0.702

Equatorial (J2000)

RA 292.21960° · Dec 44.61737°

Galactic ℓ, b

76.917° · 12.547°

Ecliptic λ, β

309.612° · 65.030°

HTM-20 index

-797492186