Key parameters at a glance

A radius of 2.08 Earth radii
A mass of 5.11 Earth masses
Surface gravity around 1.18 g
An orbital period of 10.055 days
Semi-major axis 0.0747 AU
Equilibrium temperature 501 K (228 °C)
Distance from Earth 143.75 light-years
Earth Similarity Index 0.532
Travel time at Voyager 1 speed 2,534,956 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

K2-3b, also known as EPIC 201367065 b, is an exoplanet orbiting the red dwarf K2-3 every 10 days. It is the largest and most massive planet of the K2-3 system, with about 2.1 times the radius of Earth and about 5 times the mass. Its density of about 3.1 g/cm3 may indicate a composition of almost entirely water, or a hydrogen envelope comprising about 0.7% of the planet's mass.

Excerpted from Wikipedia · full article

2 siblings around K2-3

K2-3 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
K2-3 b this	Sub-Neptune	2.08	5.11	10.055	501	2015
K2-3 c	Super-Earth	1.58	2.68	24.647	372	2015
K2-3 d	Super-Earth	1.46	2.20	44.556	305	2015

K2-3 b Planet Profile

Physical Specs

Radius

2.08 R⊕

Radius (Jupiter)

0.185 R♃

Mass

5.11 M⊕

Mass (Jupiter)

0.016 M♃

Density

3.11 g/cm³

Surface Gravity

1.18 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.532

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

#1857of 1978

top 93.8%

This planet

2.08R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

TOI-1801 b 2.08 R⊕ Kepler-237 c 2.08 R⊕ Kepler-405 b 2.08 R⊕

Metric	Earth	K2-3 b	Jupiter
Radius (R⊕)	1.00	2.08	11.21
Mass (M⊕)	1.00	5.11	317.83
Density (g/cm³)	5.51	3.11	1.33
Surface Gravity (g)	1.00	1.18	2.53
Insolation (S⊕)	1.00	10.50	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	5.110 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 173103335

Gaia DR2

Gaia DR2 3796690380302214272

Gaia DR3

Gaia DR3 3796690380302214272

System

K2-3

Percentile among Sub-Neptune cohort

Radius 2.078 R⊕ · percentile 6 / cohort 1978

Mass 5.110 M⊕ · percentile 10 / cohort 1978

Orbital period 10.05 d · percentile 34 / cohort 1946

Distance 44.07 pc · percentile 11 / cohort 1975

ESI 0.532 · percentile 74 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

10.055 days

Semi-major axis

0.0747 AU

Eccentricity

0.107

Inclination

89.40 °

Year Length

A year here lasts approximately 10.05 Earth days (2.8% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0747 AU.

Transit Fingerprint

Depth

0.142 %

Duration

2.563 h

Impact parameter b

0.310

Rp / R★

0.034900

Transit midpoint (BJD)

2,457,165.3295

Photometric dip

Transit produces a flux drop of 1,416 ppm lasting ≈ 2.56 h.

Extended Orbital Architecture

Planet / star radius ratio

0.034900

Semi-major axis / stellar radius

29.440

Impact parameter (b)

0.310

RV semi-amplitude (K)

2.270 m/s

Transit mid-time (BJD)

2,457,165.3295

Long. of periastron (ω)

188.00°

Angular separation (arcsec)

1.69000

Eq. Temperature

501K

(228 °C)

Insolation (S⊕)

10.50

Earth = 1.00

Earth Similarity (ESI)

0.532

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.

Radial velocity

Stellar wobble has been measured spectroscopically.

Discovery Paper

Primary reference

Crossfield et al. 2015

Instrument

Kepler CCD Array

Publication

2015-05

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 K2-17 b · Sub-Neptune K2-21 b · Super-Earth K2-16 c · Sub-Neptune K2-5 b · Super-Earth K2-25 b · Sub-Neptune

Host System: K2-3

Spectral Class

M-type red dwarf

Effective Temperature

3,844 K — cooler than the Sun (5,778 K)

Estimated Age

6.90 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.546 R☉

Stellar Mass

0.549 M☉

Metallicity [Fe/H]

-0.16

Extended Stellar Properties

Surface gravity (log g)

4.704 dex

Stellar density

4.780 g/cm³

Systemic radial velocity

30.48 km/s

Rotation period

40.71 days

Metallicity ratio

[Fe/H]

Distance

44.07 parsec

Light-years 143.75 ly

V-band magnitude

12.17 mag

Voyager-speed travel 2,534,956 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

22.661 mas

Total Proper Motion

122.262 mas/yr

PM Right Ascension

94.03 mas/yr

PM Declination

-78.14 mas/yr

Galactic Cartesian (pc)

x = -0.991 · y = 0.133 · z = -0.025

Equatorial (J2000)

RA 172.33537° · Dec -1.45514°

Galactic ℓ, b

264.988° · 55.250°

Ecliptic λ, β

173.533° · -4.378°

HTM-20 index

-116781740

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