Key parameters at a glance

A radius of 2.44 Earth radii
A mass of 5.20 Earth masses
Surface gravity around 0.87 g
An orbital period of 8.282 days
Semi-major axis 0.0792 AU
Equilibrium temperature 1,026 K (753 °C)
Distance from Earth 1,064.51 light-years
Earth Similarity Index 0.228
Travel time at Voyager 1 speed 18,772,654 years

K2-12 b Planet Profile

Physical Specs

Radius

2.44 R⊕

Radius (Jupiter)

0.218 R♃

Mass

5.20 M⊕

Mass (Jupiter)

0.016 M♃

Density

1.60 g/cm³

Surface Gravity

0.87 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.228

HZ Position Inner

Controversial No

Discovery

Year 2015

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1269of 1978

top 64.1%

This planet

2.44R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-338 b 2.44 R⊕ Kepler-1086 b 2.44 R⊕ HD 106315 b 2.44 R⊕

Metric	Earth	K2-12 b	Jupiter
Radius (R⊕)	1.00	2.44	11.21
Mass (M⊕)	1.00	5.20	317.83
Density (g/cm³)	5.51	1.60	1.33
Surface Gravity (g)	1.00	0.87	2.53
Insolation (S⊕)	1.00	185.00	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	5.200 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 396972464

Gaia DR2

Gaia DR2 3800129201701685504

Gaia DR3

Gaia DR3 3800129201701685504

System

K2-12

Percentile among Sub-Neptune cohort

Radius 2.440 R⊕ · percentile 36 / cohort 1978

Mass 5.200 M⊕ · percentile 12 / cohort 1978

Orbital period 8.28 d · percentile 27 / cohort 1946

Distance 326.38 pc · percentile 37 / cohort 1975

ESI 0.228 · percentile 12 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

8.282 days

Semi-major axis

0.0792 AU

Eccentricity

0.500

Inclination

87.60 °

Year Length

A year here lasts approximately 8.28 Earth days (2.3% of a terrestrial year) on a highly eccentric trajectory at a mean orbital distance of 0.0792 AU.

Transit Fingerprint

Depth

0.048 %

Duration

4.180 h

Impact parameter b

0.190

Rp / R★

0.018700

Transit midpoint (BJD)

2,456,815.3701

Photometric dip

Transit produces a flux drop of 481 ppm lasting ≈ 4.18 h.

Extended Orbital Architecture

Planet / star radius ratio

0.018700

Semi-major axis / stellar radius

13.700

Impact parameter (b)

0.190

RV semi-amplitude (K)

2.100 m/s

Transit mid-time (BJD)

2,456,815.3701

Angular separation (arcsec)

0.24300

Eq. Temperature

1,026K

(753 °C)

Insolation (S⊕)

185.00

Earth = 1.00

Earth Similarity (ESI)

0.228

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Radial velocity

Stellar wobble has been measured spectroscopically.

Discovery Paper

Primary reference

Montet et al. 2015

Instrument

Kepler CCD Array

Publication

2015-08

Observation locale

Space

Discovery cohort

Planets confirmed in 2015 at K2 (12 shown).

K2-18 b · Sub-Neptune K2-9 b · Sub-Neptune K2-3 d · Super-Earth K2-3 c · Super-Earth K2-21 c · Sub-Neptune K2-5 c · Sub-Neptune K2-13 b · Super-Earth K2-3 b · Sub-Neptune K2-17 b · Sub-Neptune K2-21 b · Super-Earth K2-16 c · Sub-Neptune K2-5 b · Super-Earth

Host System: K2-12

Spectral Class

F-type yellow-white

Effective Temperature

5,672 K — cooler than the Sun (5,778 K)

Estimated Age

8.90 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

1.117 R☉

Stellar Mass

0.965 M☉

Metallicity [Fe/H]

0.00

Extended Stellar Properties

Surface gravity (log g)

4.300 dex

Stellar density

0.846 g/cm³

Systemic radial velocity

18.85 km/s

Metallicity ratio

[Fe/H]

Distance

326.38 parsec

Light-years 1,064.51 ly

V-band magnitude

12.38 mag

Voyager-speed travel 18,772,654 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

3.036 mas

Total Proper Motion

59.372 mas/yr

PM Right Ascension

-35.12 mas/yr

PM Declination

-47.87 mas/yr

Galactic Cartesian (pc)

x = -0.992 · y = 0.118 · z = 0.039

Equatorial (J2000)

RA 173.19190° · Dec 2.24468°

Galactic ℓ, b

262.463° · 58.791°

Ecliptic λ, β

172.858° · -0.641°

HTM-20 index

-855847882