Key parameters at a glance
- A radius of 9.11 Earth radii
- A mass of 123.00 Earth masses
- Surface gravity around 1.48 g
- An orbital period of 28.381 days
- Semi-major axis 0.1796 AU
- Equilibrium temperature 524 K (251 °C)
- Distance from Earth 501.81 light-years
- Earth Similarity Index 0.302
- Travel time at Voyager 1 speed 8,849,429 years
- Almost certainly tidally locked to its host star given the close orbit
K2-139 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#78of 574
top 13.4%
This planet
9.11R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | K2-139 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 9.11 | 11.21 |
| Mass (M⊕) | 1.00 | 123.00 | 317.83 |
| Density (g/cm³) | 5.51 | 0.91 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.48 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 123.000 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 11023038
Gaia DR2
Gaia DR2 4084602654011029376
Gaia DR3
Gaia DR3 4084602654011029376
System
K2-139
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 28.38 Earth days (7.8% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1796 AU.
Transit Fingerprint
Depth
1.109 %
Duration
4.939 h
Impact parameter b
0.170
Rp / R★
0.095100
Transit midpoint (BJD)
2,457,325.8175
Photometric dip
Transit produces a flux drop of 11,093 ppm lasting ≈ 4.94 h.
Extended Orbital Architecture
Planet / star radius ratio
0.095100
Semi-major axis / stellar radius
47.250
Impact parameter (b)
0.170
RV semi-amplitude (K)
27.700 m/s
Transit mid-time (BJD)
2,457,325.8175
Long. of periastron (ω)
124.00°
Angular separation (arcsec)
1.17000
Eq. Temperature
524K
(251 °C)
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.302
0 = alien, 1 = Earth-identical
Insufficient insolation data — 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
Barrag Aacute N et al. 2018Instrument
Kepler CCD Array
Publication
2018-04
Observation locale
Space
Discovery cohort
Planets confirmed in 2017 at K2 (12 shown).
Host System: K2-139
Spectral Class
K-type orange
Effective Temperature
5,370 K — cooler than the Sun (5,778 K)
Estimated Age
1.80 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
0.880 R☉
Stellar Mass
0.960 M☉
Metallicity [Fe/H]
0.24
Extended Stellar Properties
Surface gravity (log g)
4.540 dex
Stellar density
2.477 g/cm³
Systemic radial velocity
-31.36 km/s
Rotational v·sin i
2.80 km/s
Rotation period
17.24 days
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
6.471 mas
Total Proper Motion
38.724 mas/yr
PM Right Ascension
37.28 mas/yr
PM Declination
-10.47 mas/yr
Galactic Cartesian (pc)
x = 0.311 · y = -0.899 · z = -0.308
Equatorial (J2000)
RA 289.06671° · Dec -17.91071°
Galactic ℓ, b
19.450° · -13.403°
Ecliptic λ, β
288.160° · 4.334°
HTM-20 index
-2143465355
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