Key parameters at a glance

A radius of 3.56 Earth radii
A mass of 12.40 Earth masses
Surface gravity around 0.98 g
An orbital period of 8.748 days
Equilibrium temperature 840 K (567 °C)
Distance from Earth 700.43 light-years
Earth Similarity Index 0.261
Travel time at Voyager 1 speed 12,352,079 years

K2-178 b Planet Profile

Physical Specs

Radius

3.56 R⊕

Radius (Jupiter)

0.317 R♃

Mass

12.40 M⊕

Mass (Jupiter)

0.039 M♃

Density

1.51 g/cm³

Surface Gravity

0.98 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.261

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

#154of 1978

top 7.7%

This planet

3.56R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

TOI-7384 b 3.56 R⊕ Kepler-734 b 3.56 R⊕ KOBE-1 c 3.56 R⊕

Metric	Earth	K2-178 b	Jupiter
Radius (R⊕)	1.00	3.56	11.21
Mass (M⊕)	1.00	12.40	317.83
Density (g/cm³)	5.51	1.51	1.33
Surface Gravity (g)	1.00	0.98	2.53
Insolation (S⊕)	1.00	117.83	0.037

Star Catalogue Identifiers

TIC

TIC 26078330

Gaia DR2

Gaia DR2 61624573016925824

Gaia DR3

Gaia DR3 61624573016925824

System

K2-178

Percentile among Sub-Neptune cohort

Radius 3.558 R⊕ · percentile 92 / cohort 1978

Mass 12.400 M⊕ · percentile 85 / cohort 1978

Orbital period 8.75 d · percentile 29 / cohort 1946

Distance 214.75 pc · percentile 30 / cohort 1975

ESI 0.261 · percentile 19 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

8.748 days

Semi-major axis

— AU

Eccentricity

—

Inclination

88.61 °

Year Length

A year here lasts approximately 8.75 Earth days (2.4% of a terrestrial year).

Transit Fingerprint

Depth

0.145 %

Duration

3.427 h

Rp / R★

0.036763

Transit midpoint (BJD)

2,457,070.3366

Photometric dip

Transit produces a flux drop of 1,449 ppm lasting ≈ 3.43 h.

Eq. Temperature

840K

(567 °C)

Insolation (S⊕)

117.83

Earth = 1.00

Earth Similarity (ESI)

0.261

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

Discovery Paper

Primary reference

Mayo 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: K2-178

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,525 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.887 R☉

Stellar Mass

0.951 M☉

Metallicity [Fe/H]

0.09

Extended Stellar Properties

Surface gravity (log g)

4.550 dex

Stellar density

2.141 g/cm³

Systemic radial velocity

0.39 km/s

Metallicity ratio

[Fe/H]

Distance

214.75 parsec

Light-years 700.43 ly

V-band magnitude

12.38 mag

Voyager-speed travel 12,352,079 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

4.628 mas

Total Proper Motion

13.177 mas/yr

PM Right Ascension

-7.59 mas/yr

PM Declination

-10.77 mas/yr

Galactic Cartesian (pc)

x = 0.558 · y = 0.737 · z = 0.382

Equatorial (J2000)

RA 52.88885° · Dec 22.43482°

Galactic ℓ, b

164.841° · -27.122°

Ecliptic λ, β

56.037° · 3.264°

HTM-20 index

-1617896305