Key parameters at a glance
- A radius of 9.27 Earth radii
- A mass of 68.97 Earth masses
- Surface gravity around 0.80 g
- An orbital period of 11.633 days
- Semi-major axis 0.1086 AU
- Equilibrium temperature 1,036 K (763 °C)
- Distance from Earth 695.64 light-years
- Earth Similarity Index 0.136
- Travel time at Voyager 1 speed 12,267,528 years
K2-261 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#63of 574
top 10.8%
This planet
9.27R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | K2-261 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 9.27 | 11.21 |
| Mass (M⊕) | 1.00 | 68.97 | 317.83 |
| Density (g/cm³) | 5.51 | 0.47 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.80 | 2.53 |
| Insolation (S⊕) | 1.00 | 180.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 68.969 M⊕ | Direct mass measurement (not derived). |
| Minimum mass (M sin i) | 70.876 M⊕ | Lower bound from radial-velocity fitting. |
| Computed mass | 70.904 M⊕ | Model-computed mass (e.g. from mass-radius relation). |
Star Catalogue Identifiers
TIC
TIC 281731203
Gaia DR2
Gaia DR2 3807826337147474176
Gaia DR3
Gaia DR3 3807826337147474176
System
K2-261
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 11.63 Earth days (3.2% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1086 AU.
Transit Fingerprint
Depth
0.278 %
Duration
5.129 h
Impact parameter b
0.290
Rp / R★
0.052740
Transit midpoint (BJD)
2,458,151.1439
Photometric dip
Transit produces a flux drop of 2,781 ppm lasting ≈ 5.13 h.
Extended Orbital Architecture
Planet / star radius ratio
0.052740
Semi-major axis / stellar radius
14.510
Impact parameter (b)
0.290
RV semi-amplitude (K)
17.400 m/s
Transit mid-time (BJD)
2,458,151.1439
Long. of periastron (ω)
145.00°
Sky-projected obliquity (λ)
32.00°
Angular separation (arcsec)
0.50900
Eq. Temperature
1,036K
(763 °C)
Insolation (S⊕)
180.00
Earth = 1.00
Earth Similarity (ESI)
0.136
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
Johnson et al. 2018Instrument
Kepler CCD Array
Publication
2018-11
Observation locale
Space
Discovery cohort
Planets confirmed in 2018 at K2 (12 shown).
Host System: K2-261
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,490 K — cooler than the Sun (5,778 K)
Estimated Age
8.80 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.663 R☉
Stellar Mass
1.107 M☉
Metallicity [Fe/H]
0.37
Extended Stellar Properties
Surface gravity (log g)
4.040 dex
Stellar density
0.339 g/cm³
Systemic radial velocity
3.28 km/s
Rotational v·sin i
1.30 km/s
Activity index (log R'HK)
-5.160
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
4.660 mas
Total Proper Motion
50.110 mas/yr
PM Right Ascension
-23.66 mas/yr
PM Declination
-44.17 mas/yr
Galactic Cartesian (pc)
x = -0.956 · y = 0.292 · z = 0.009
Equatorial (J2000)
RA 163.03231° · Dec 0.49317°
Galactic ℓ, b
250.883° · 50.895°
Ecliptic λ, β
164.167° · -6.211°
HTM-20 index
1104842063
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