Key parameters at a glance
- A radius of 2.35 Earth radii
- A mass of 6.12 Earth masses
- Surface gravity around 1.11 g
- An orbital period of 9.301 days
- Semi-major axis 0.0694 AU
- Equilibrium temperature 437 K (164 °C)
- Distance from Earth 479.55 light-years
- Earth Similarity Index 0.571
- Travel time at Voyager 1 speed 8,456,814 years
- Almost certainly tidally locked to its host star given the close orbit
K2-251 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1416of 1978
top 71.5%
This planet
2.35R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | K2-251 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.35 | 11.21 |
| Mass (M⊕) | 1.00 | 6.12 | 317.83 |
| Density (g/cm³) | 5.51 | 2.59 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.11 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Star Catalogue Identifiers
TIC
TIC 156584871
Gaia DR2
Gaia DR2 3675248118423392256
Gaia DR3
Gaia DR3 3675248118423392256
System
K2-251
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 9.30 Earth days (2.5% of a terrestrial year) at a mean orbital distance of 0.0694 AU.
Transit Fingerprint
Depth
0.214 %
Duration
2.700 h
Impact parameter b
0.440
Rp / R★
0.043700
Transit midpoint (BJD)
2,457,589.0782
Photometric dip
Transit produces a flux drop of 2,140 ppm lasting ≈ 2.70 h.
Extended Orbital Architecture
Planet / star radius ratio
0.043700
Semi-major axis / stellar radius
20.600
Impact parameter (b)
0.440
Transit mid-time (BJD)
2,457,589.0782
Angular separation (arcsec)
0.47200
Eq. Temperature
437K
(164 °C)
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.571
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.
Discovery Paper
Primary reference
Livingston et al. 2018Instrument
Kepler CCD Array
Publication
2018-08
Observation locale
Space
Discovery cohort
Planets confirmed in 2018 at K2 (12 shown).
Host System: K2-251
Spectral Class
K-type orange
Effective Temperature
3,717 K — cooler than the Sun (5,778 K)
Estimated Age
—
Stellar Radius
0.490 R☉
Stellar Mass
0.520 M☉
Metallicity [Fe/H]
-0.04
Extended Stellar Properties
Surface gravity (log g)
4.760 dex
Stellar density
5.744 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
6.773 mas
Total Proper Motion
21.082 mas/yr
PM Right Ascension
10.96 mas/yr
PM Declination
-18.01 mas/yr
Galactic Cartesian (pc)
x = -0.972 · y = -0.183 · z = -0.148
Equatorial (J2000)
RA 190.68924° · Dec -8.53598°
Galactic ℓ, b
299.255° · 54.274°
Ecliptic λ, β
193.163° · -3.625°
HTM-20 index
1775857545
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