Key parameters at a glance

A radius of 2.25 Earth radii
A mass of 5.69 Earth masses
Surface gravity around 1.12 g
An orbital period of 18.450 days
Semi-major axis 0.0910 AU
Equilibrium temperature 314 K (41 °C)
Distance from Earth 270.59 light-years
Earth Similarity Index 0.752
Travel time at Voyager 1 speed 4,771,839 years
Almost certainly tidally locked to its host star given the close orbit

K2-9 b Planet Profile

Physical Specs

Radius

2.25 R⊕

Radius (Jupiter)

0.201 R♃

Mass

5.69 M⊕

Mass (Jupiter)

0.018 M♃

Density

2.74 g/cm³

Surface Gravity

1.12 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.752

HZ Position Habitable

Controversial No

Discovery

Year 2015

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1589of 1978

top 80.3%

This planet

2.25R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-300 c 2.25 R⊕ GJ 667 C b 2.25 R⊕ Kepler-342 b 2.25 R⊕

Metric	Earth	K2-9 b	Jupiter
Radius (R⊕)	1.00	2.25	11.21
Mass (M⊕)	1.00	5.69	317.83
Density (g/cm³)	5.51	2.74	1.33
Surface Gravity (g)	1.00	1.12	2.53
Insolation (S⊕)	1.00	1.36	0.037

Star Catalogue Identifiers

TIC

TIC 82050863

Gaia DR2

Gaia DR2 3795633852707093120

Gaia DR3

Gaia DR3 3795633852707093120

System

K2-9

Percentile among Sub-Neptune cohort

Radius 2.250 R⊕ · percentile 19 / cohort 1978

Mass 5.690 M⊕ · percentile 19 / cohort 1978

Orbital period 18.45 d · percentile 59 / cohort 1946

Distance 82.96 pc · percentile 18 / cohort 1975

ESI 0.752 · percentile 97 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

18.450 days

Semi-major axis

0.0910 AU

Eccentricity

—

Inclination

87.98 °

Year Length

A year here lasts approximately 18.45 Earth days (5.1% of a terrestrial year) at a mean orbital distance of 0.0910 AU.

Transit Fingerprint

Depth

0.399 %

Duration

2.840 h

Impact parameter b

0.926

Rp / R★

0.066690

Transit midpoint (BJD)

2,456,822.6712

Photometric dip

Transit produces a flux drop of 3,990 ppm lasting ≈ 2.84 h.

Extended Orbital Architecture

Planet / star radius ratio

0.066690

Semi-major axis / stellar radius

26.300

Impact parameter (b)

0.926

Transit mid-time (BJD)

2,456,822.6712

Angular separation (arcsec)

1.10000

Eq. Temperature

314K

(41 °C)

Insolation (S⊕)

1.36

Earth = 1.00

Earth Similarity (ESI)

0.752

0 = alien, 1 = Earth-identical

Within the conservative habitable zone — liquid water is physically possible with adequate atmospheric pressure. Close-orbiting tidally-locked around a cool host.

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 K2-3 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 K2-25 b · Sub-Neptune

Host System: K2-9

Spectral Class

M-type red dwarf

Effective Temperature

3,390 K — cooler than the Sun (5,778 K)

Estimated Age

1.00 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.310 R☉

Stellar Mass

0.300 M☉

Metallicity [Fe/H]

-0.25

Extended Stellar Properties

Surface gravity (log g)

4.816 dex

Stellar density

9.880 g/cm³

Systemic radial velocity

-31.02 km/s

Metallicity ratio

[Fe/H]

Distance

82.96 parsec

Light-years 270.59 ly

V-band magnitude

15.86 mag

Voyager-speed travel 4,771,839 yr

Multi-band Host Photometry — 14 bands

Astrometric Data

Parallax

12.025 mas

Total Proper Motion

172.816 mas/yr

PM Right Ascension

-170.75 mas/yr

PM Declination

26.63 mas/yr

Galactic Cartesian (pc)

x = -0.998 · y = 0.065 · z = 0.000

Equatorial (J2000)

RA 176.26372° · Dec 0.00541°

Galactic ℓ, b

269.758° · 58.535°

Ecliptic λ, β

176.565° · -1.480°

HTM-20 index

-1718011793

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