Key parameters at a glance
- A radius of 2.28 Earth radii
- A mass of 7.50 Earth masses
- Surface gravity around 1.45 g
- An orbital period of 15.389 days
- Semi-major axis 0.1186 AU
- Equilibrium temperature 803 K (530 °C)
- Distance from Earth 330.46 light-years
- Earth Similarity Index 0.340
- Travel time at Voyager 1 speed 5,827,741 years
K2-222 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1550of 1978
top 78.3%
This planet
2.28R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | K2-222 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.28 | 11.21 |
| Mass (M⊕) | 1.00 | 7.50 | 317.83 |
| Density (g/cm³) | 5.51 | 3.72 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.45 | 2.53 |
| Insolation (S⊕) | 1.00 | 95.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 7.500 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 257774438
Gaia DR2
Gaia DR2 2584093844170270720
Gaia DR3
Gaia DR3 2584093844170270720
System
K2-222
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 15.39 Earth days (4.2% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1186 AU.
Transit Fingerprint
Depth
0.037 %
Duration
4.382 h
Impact parameter b
0.451
Rp / R★
0.019500
Transit midpoint (BJD)
2,459,491.9547
Photometric dip
Transit produces a flux drop of 372 ppm lasting ≈ 4.38 h.
Extended Orbital Architecture
Planet / star radius ratio
0.019500
Semi-major axis / stellar radius
24.000
Impact parameter (b)
0.451
RV semi-amplitude (K)
2.010 m/s
Transit mid-time (BJD)
2,459,491.9547
Angular separation (arcsec)
1.17000
Eq. Temperature
803K
(530 °C)
Insolation (S⊕)
95.00
Earth = 1.00
Earth Similarity (ESI)
0.340
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.
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
Mayo et al. 2018Instrument
Kepler CCD Array
Publication
2018-03
Observation locale
Space
Discovery cohort
Planets confirmed in 2018 at K2 (12 shown).
Host System: K2-222
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,942 K — hotter than the Sun (5,778 K)
Estimated Age
7.10 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.072 R☉
Stellar Mass
0.940 M☉
Metallicity [Fe/H]
-0.32
Extended Stellar Properties
Surface gravity (log g)
4.350 dex
Stellar density
1.071 g/cm³
Systemic radial velocity
1.48 km/s
Rotational v·sin i
3.10 km/s
Activity index (log R'HK)
-5.128
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
9.841 mas
Total Proper Motion
86.964 mas/yr
PM Right Ascension
55.30 mas/yr
PM Declination
67.12 mas/yr
Galactic Cartesian (pc)
x = 0.939 · y = 0.277 · z = 0.204
Equatorial (J2000)
RA 16.46252° · Dec 11.75372°
Galactic ℓ, b
128.538° · -50.961°
Ecliptic λ, β
19.664° · 4.389°
HTM-20 index
1677731310
Similar Worlds
K2-398 b
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.27 R⊕ · 1,979.7 ly
Kepler-1817 b
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.27 R⊕ · 2,441.5 ly
TOI-5788 c
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.27 R⊕ · 318.4 ly
Kepler-1766 b
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.28 R⊕ · 1,634.8 ly
Kepler-1985 b
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.27 R⊕ · —
Kepler-166 b
Sub-Neptune · G-type yellow (Sun-like)
Radius 2.27 R⊕ · 1,968.4 ly