Key parameters at a glance

A radius of 0.57 Earth radii
A mass of 0.36 Earth masses
Surface gravity around 1.10 g
An orbital period of 1.865 days
Semi-major axis 0.0154 AU
Equilibrium temperature 450 K (177 °C)
Distance from Earth 130.66 light-years
Earth Similarity Index 0.419
Travel time at Voyager 1 speed 2,304,127 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

Kepler-42, formerly known as KOI-961, is a red dwarf located in the constellation Cygnus and approximately 131 light years from the Sun. It has three known extrasolar planets, all of which are smaller than Earth in radius and orbit very close to the star.

Excerpted from Wikipedia · full article

2 siblings around Kepler-42

Kepler-42 d 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	Rocky Terrestrial	0.78	0.71	1.214	519	2011
Kepler-42 d this	Rocky Terrestrial	0.57	0.36	1.865	450	2011

Kepler-42 d Planet Profile

Physical Specs

Radius

0.57 R⊕

Radius (Jupiter)

0.051 R♃

Mass

0.36 M⊕

Mass (Jupiter)

0.001 M♃

Density

0.55 g/cm³

Surface Gravity

1.10 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.419

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

#553of 570

top 96.8%

This planet

0.57R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-102 c 0.57 R⊕ GJ 238 b 0.57 R⊕ Kepler-444 e 0.55 R⊕

Metric	Earth	Kepler-42 d	Jupiter
Radius (R⊕)	1.00	0.57	11.21
Mass (M⊕)	1.00	0.36	317.83
Density (g/cm³)	5.51	0.55	1.33
Surface Gravity (g)	1.00	1.10	2.53
Insolation (S⊕)	1.00	12.54	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.358 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 0.570 R⊕ · percentile 3 / cohort 570

Mass 0.358 M⊕ · percentile 9 / cohort 570

Orbital period 1.87 d · percentile 20 / cohort 567

Distance 40.06 pc · percentile 17 / cohort 566

ESI 0.419 · percentile 62 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

1.865 days

Semi-major axis

0.0154 AU

Eccentricity

0.020

Inclination

88.02 °

Year Length

A year here lasts approximately 1.87 Earth days (0.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0154 AU.

Transit Fingerprint

Depth

0.112 %

Duration

0.428 h

Impact parameter b

0.681

Rp / R★

0.030700

Transit midpoint (BJD)

2,454,966.7847

Photometric dip

Transit produces a flux drop of 1,125 ppm lasting ≈ 0.43 h.

Extended Orbital Architecture

Planet / star radius ratio

0.030700

Semi-major axis / stellar radius

37.020

Impact parameter (b)

0.681

Transit mid-time (BJD)

2,454,966.7847

Angular separation (arcsec)

0.38400

Eq. Temperature

450K

(177 °C)

Insolation (S⊕)

12.54

Earth = 1.00

Earth Similarity (ESI)

0.419

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-16 b · Neptune-like Kepler-28 b · Super-Earth Kepler-34 b · Neptune-like Kepler-29 c · Sub-Neptune

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

Wikipedia → Image: Wikimedia Commons · NASA/JPL-Caltech · Public domain