Key parameters at a glance
- A radius of 6.28 Earth radii
- A mass of 28.60 Earth masses
- Surface gravity around 0.73 g
- An orbital period of 4.605 days
- Semi-major axis 0.0571 AU
- Equilibrium temperature 1,670 K (1397 °C)
- Distance from Earth 1,002.83 light-years
- Earth Similarity Index 0.100
- Travel time at Voyager 1 speed 17,684,939 years
- Almost certainly tidally locked to its host star given the close orbit
K2-39 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#256of 574
top 44.4%
This planet
6.28R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | K2-39 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 6.28 | 11.21 |
| Mass (M⊕) | 1.00 | 28.60 | 317.83 |
| Density (g/cm³) | 5.51 | 0.93 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.73 | 2.53 |
| Insolation (S⊕) | 1.00 | 1,356.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 28.605 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 250977648
Gaia DR2
Gaia DR2 2609222216055014144
Gaia DR3
Gaia DR3 2609222216055014144
System
K2-39
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 4.61 Earth days (1.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0571 AU.
Transit Fingerprint
Depth
0.037 %
Duration
8.184 h
Impact parameter b
0.570
Rp / R★
0.019250
Transit midpoint (BJD)
2,456,985.4268
Photometric dip
Transit produces a flux drop of 370 ppm lasting ≈ 8.18 h.
Extended Orbital Architecture
Planet / star radius ratio
0.019250
Semi-major axis / stellar radius
3.410
Impact parameter (b)
0.570
RV semi-amplitude (K)
14.400 m/s
Transit mid-time (BJD)
2,456,985.4268
Angular separation (arcsec)
0.18600
Eq. Temperature
1,670K
(1397 °C)
Insolation (S⊕)
1,356.00
Earth = 1.00
Earth Similarity (ESI)
0.100
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched. 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
Van Eylen et al. 2016Instrument
Kepler CCD Array
Publication
2016-11
Observation locale
Space
Discovery cohort
Planets confirmed in 2016 at K2 (12 shown).
Host System: K2-39
Spectral Class
K-type orange
Effective Temperature
4,881 K — cooler than the Sun (5,778 K)
Estimated Age
6.70 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
2.970 R☉
Stellar Mass
0.660 M☉
Metallicity [Fe/H]
0.32
Extended Stellar Properties
Surface gravity (log g)
3.440 dex
Stellar density
0.040 g/cm³
Systemic radial velocity
24.35 km/s
Rotational v·sin i
2.01 km/s
Activity index (log R'HK)
-5.060
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 17 bands
Astrometric Data
Parallax
3.224 mas
Total Proper Motion
56.738 mas/yr
PM Right Ascension
-40.95 mas/yr
PM Declination
-39.27 mas/yr
Galactic Cartesian (pc)
x = 0.918 · y = -0.364 · z = -0.157
Equatorial (J2000)
RA 338.36821° · Dec -9.02294°
Galactic ℓ, b
55.427° · -52.747°
Ecliptic λ, β
336.642° · 0.053°
HTM-20 index
-969136989
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