Key parameters at a glance

A radius of 2.05 Earth radii
A mass of 5.77 Earth masses
Surface gravity around 1.37 g
An orbital period of 2.645 days
Semi-major axis 0.0248 AU
Equilibrium temperature 534 K (261 °C)
Distance from Earth 258.64 light-years
Earth Similarity Index 0.514
Travel time at Voyager 1 speed 4,561,158 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

K2-146b is a Neptune-like exoplanet discovered in 2018 by the Kepler Space Telescope that orbits a low-mass M-type star in the constellation Cancer. Its host star, K2-146, is orbited by another planet named K2-146c. The planet orbits K2-146 at a distance of 0.0248 AU (3,710,000 km), fifteen times closer than Mercury is to the Sun. Thus, it orbits very rapidly, with one year lasting just 2.64 days, and is far too hot to be habitable, with an equilibrium temperature of 534 K.

Excerpted from Wikipedia · full article

1 sibling around K2-146

K2-146 b 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
K2-146 b this	Sub-Neptune	2.05	5.77	2.645	534	2018
K2-146 c	Sub-Neptune	2.19	7.49	4.005	—	2019

K2-146 b Planet Profile

Physical Specs

Radius

2.05 R⊕

Radius (Jupiter)

0.183 R♃

Mass

5.77 M⊕

Mass (Jupiter)

0.018 M♃

Density

3.69 g/cm³

Surface Gravity

1.37 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.514

HZ Position Inner

Controversial No

Discovery

Year 2018

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1888of 1978

top 95.4%

This planet

2.05R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-337 c 2.05 R⊕ Kepler-244 c 2.05 R⊕ Kepler-363 d 2.05 R⊕

Metric	Earth	K2-146 b	Jupiter
Radius (R⊕)	1.00	2.05	11.21
Mass (M⊕)	1.00	5.77	317.83
Density (g/cm³)	5.51	3.69	1.33
Surface Gravity (g)	1.00	1.37	2.53
Insolation (S⊕)	1.00	20.70	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	5.770 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 175261852

Gaia DR2

Gaia DR2 661192902209491456

Gaia DR3

Gaia DR3 661192902209491456

System

K2-146

Percentile among Sub-Neptune cohort

Radius 2.050 R⊕ · percentile 4 / cohort 1978

Mass 5.770 M⊕ · percentile 21 / cohort 1978

Orbital period 2.64 d · percentile 4 / cohort 1946

Distance 79.30 pc · percentile 17 / cohort 1975

ESI 0.514 · percentile 72 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

2.645 days

Semi-major axis

0.0248 AU

Eccentricity

0.129

Inclination

88.93 °

Year Length

A year here lasts approximately 2.64 Earth days (0.7% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0248 AU.

Transit Fingerprint

Depth

0.386 %

Duration

1.320 h

Impact parameter b

0.391

Rp / R★

0.057200

Transit midpoint (BJD)

2,458,204.5902

Photometric dip

Transit produces a flux drop of 3,860 ppm lasting ≈ 1.32 h.

Extended Orbital Architecture

Planet / star radius ratio

0.057200

Semi-major axis / stellar radius

15.250

Impact parameter (b)

0.391

Transit mid-time (BJD)

2,458,204.5902

Long. of periastron (ω)

-64.00°

Angular separation (arcsec)

0.31300

Eq. Temperature

534K

(261 °C)

Insolation (S⊕)

20.70

Earth = 1.00

Earth Similarity (ESI)

0.514

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

Hirano et al. 2018

Instrument

Kepler CCD Array

Publication

2018-03

Observation locale

Space

Discovery cohort

Planets confirmed in 2018 at K2 (12 shown).

K2-190 c · Rocky Terrestrial K2-183 b · Rocky Terrestrial K2-209 b · Rocky Terrestrial K2-210 b · Rocky Terrestrial K2-165 b · Super-Earth K2-169 b · Super-Earth K2-148 b · Super-Earth K2-219 b · Super-Earth K2-190 b · Super-Earth K2-200 b · Super-Earth K2-201 b · Super-Earth K2-170 b · Super-Earth

Host System: K2-146

Spectral Class

M-type red dwarf

Effective Temperature

3,385 K — cooler than the Sun (5,778 K)

Estimated Age

5.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.330 R☉

Stellar Mass

0.331 M☉

Metallicity [Fe/H]

-0.02

Extended Stellar Properties

Surface gravity (log g)

4.898 dex

Stellar density

13.100 g/cm³

Systemic radial velocity

40.60 km/s

Rotational v·sin i

2.00 km/s

Metallicity ratio

[Fe/H]

Distance

79.30 parsec

Light-years 258.64 ly

V-band magnitude

16.70 mag

Voyager-speed travel 4,561,158 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

12.582 mas

Total Proper Motion

129.998 mas/yr

PM Right Ascension

-15.92 mas/yr

PM Declination

-129.02 mas/yr

Galactic Cartesian (pc)

x = -0.608 · y = 0.724 · z = 0.327

Equatorial (J2000)

RA 130.02670° · Dec 19.09234°

Galactic ℓ, b

206.528° · 32.219°

Ecliptic λ, β

127.428° · 0.702°

HTM-20 index

62696340

Wikipedia → Image: Wikimedia Commons · Martin Vargic / Halcyon Maps · CC BY 3.0