Key parameters at a glance
- A radius of 5.33 Earth radii
- A mass of 59.40 Earth masses
- Surface gravity around 2.09 g
- An orbital period of 4.734 days
- Semi-major axis 0.0581 AU
- Equilibrium temperature 1,360 K (1087 °C)
- Distance from Earth 1,556.73 light-years
- Earth Similarity Index 0.147
- Travel time at Voyager 1 speed 27,452,866 years
K2-108 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#339of 574
top 58.9%
This planet
5.33R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | K2-108 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 5.33 | 11.21 |
| Mass (M⊕) | 1.00 | 59.40 | 317.83 |
| Density (g/cm³) | 5.51 | 2.22 | 1.33 |
| Surface Gravity (g) | 1.00 | 2.09 | 2.53 |
| Insolation (S⊕) | 1.00 | 762.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 59.400 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 27635334
Gaia DR2
Gaia DR2 655794055300531456
Gaia DR3
Gaia DR3 655794055300531456
System
K2-108
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 4.73 Earth days (1.3% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0581 AU.
Transit Fingerprint
Depth
0.097 %
Duration
3.550 h
Impact parameter b
0.330
Rp / R★
0.027700
Transit midpoint (BJD)
2,457,145.0961
Photometric dip
Transit produces a flux drop of 973 ppm lasting ≈ 3.55 h.
Extended Orbital Architecture
Planet / star radius ratio
0.027700
Semi-major axis / stellar radius
9.860
Impact parameter (b)
0.330
RV semi-amplitude (K)
21.300 m/s
Transit mid-time (BJD)
2,457,145.0961
Angular separation (arcsec)
0.12200
Eq. Temperature
1,360K
(1087 °C)
Insolation (S⊕)
762.00
Earth = 1.00
Earth Similarity (ESI)
0.147
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
Petigura et al. 2017Instrument
Kepler CCD Array
Publication
2017-04
Observation locale
Space
Discovery cohort
Planets confirmed in 2017 at K2 (12 shown).
Host System: K2-108
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,599 K — cooler than the Sun (5,778 K)
Estimated Age
7.80 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.760 R☉
Stellar Mass
1.170 M☉
Metallicity [Fe/H]
0.36
Extended Stellar Properties
Surface gravity (log g)
4.020 dex
Stellar density
0.806 g/cm³
Rotational v·sin i
2.83 km/s
Activity index (log R'HK)
-5.293
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 17 bands
Astrometric Data
Parallax
2.067 mas
Total Proper Motion
23.740 mas/yr
PM Right Ascension
-6.87 mas/yr
PM Declination
-22.72 mas/yr
Galactic Cartesian (pc)
x = -0.528 · y = 0.801 · z = 0.283
Equatorial (J2000)
RA 123.38185° · Dec 16.41952°
Galactic ℓ, b
206.691° · 25.352°
Ecliptic λ, β
121.914° · -3.398°
HTM-20 index
-1691712073
Similar Worlds
TOI-2019 b
Neptune-like · G-type yellow (Sun-like)
Radius 5.33 R⊕ · 645.8 ly
K2-403 b
Neptune-like · G-type yellow (Sun-like)
Radius 5.33 R⊕ · 804.3 ly
Kepler-82 c
Neptune-like · G-type yellow (Sun-like)
Radius 5.34 R⊕ · 2,949.5 ly
Kepler-33 d
Neptune-like · G-type yellow (Sun-like)
Radius 5.35 R⊕ · 3,943.7 ly
Kepler-281 c
Neptune-like · G-type yellow (Sun-like)
Radius 5.31 R⊕ · 5,692.9 ly
TOI-5174 b
Neptune-like · G-type yellow (Sun-like)
Radius 5.35 R⊕ · 643.3 ly