Key parameters at a glance
- A radius of 2.42 Earth radii
- A mass of 17.20 Earth masses
- Surface gravity around 2.94 g
- An orbital period of 5.955 days
- Semi-major axis 0.0522 AU
- Equilibrium temperature 635 K (362 °C)
- Distance from Earth 1,135.97 light-years
- Earth Similarity Index 0.420
- Travel time at Voyager 1 speed 20,032,865 years
- Almost certainly tidally locked to its host star given the close orbit
2 siblings around Kepler-81
Kepler-81 b shares its host star with 2 other confirmed planets. Side-by-side measurements below.
| Planet | Type | Radius (R⊕) | Mass (M⊕) | Period (d) | Eq. T (K) | Year |
|---|---|---|---|---|---|---|
| Kepler-81 b this | Sub-Neptune | 2.42 | 17.20 | 5.955 | 635 | 2012 |
| Kepler-81 c | Sub-Neptune | 2.37 | 4.30 | 12.040 | 502 | 2012 |
| Kepler-81 d | Rocky Terrestrial | 1.21 | 1.92 | 20.838 | 418 | 2014 |
Kepler-81 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1299of 1978
top 65.6%
This planet
2.42R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | Kepler-81 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.42 | 11.21 |
| Mass (M⊕) | 1.00 | 17.20 | 317.83 |
| Density (g/cm³) | 5.51 | 6.67 | 1.33 |
| Surface Gravity (g) | 1.00 | 2.94 | 2.53 |
| Insolation (S⊕) | 1.00 | 39.95 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 17.200 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 270611154
Gaia DR2
Gaia DR2 2077816087307845248
Gaia DR3
Gaia DR3 2077816087307845248
System
Kepler-81
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 5.96 Earth days (1.6% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0522 AU.
Transit Fingerprint
Depth
0.151 %
Duration
2.369 h
Impact parameter b
0.810
Rp / R★
0.034923
Transit midpoint (BJD)
2,455,003.9581
Photometric dip
Transit produces a flux drop of 1,505 ppm lasting ≈ 2.37 h.
Extended Orbital Architecture
Planet / star radius ratio
0.034923
Semi-major axis / stellar radius
19.882
Impact parameter (b)
0.810
Transit mid-time (BJD)
2,455,003.9581
Angular separation (arcsec)
0.15000
Eq. Temperature
635K
(362 °C)
Insolation (S⊕)
39.95
Earth = 1.00
Earth Similarity (ESI)
0.420
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — 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.
Transit timing variations
Gravitational interactions from neighbours have been detected.
Discovery Paper
Discovery cohort
Planets confirmed in 2012 at Kepler (12 shown).
Host System: Kepler-81
Spectral Class
M-type red dwarf
Effective Temperature
4,385 K — cooler than the Sun (5,778 K)
Estimated Age
3.63 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
0.590 R☉
Stellar Mass
0.640 M☉
Metallicity [Fe/H]
-0.18
Extended Stellar Properties
Surface gravity (log g)
4.700 dex
Stellar density
4.193 g/cm³
Metallicity ratio
[M/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
2.843 mas
Total Proper Motion
24.701 mas/yr
PM Right Ascension
-1.37 mas/yr
PM Declination
-24.66 mas/yr
Galactic Cartesian (pc)
x = 0.294 · y = -0.672 · z = 0.680
Equatorial (J2000)
RA 293.63694° · Dec 42.82483°
Galactic ℓ, b
75.746° · 10.830°
Ecliptic λ, β
310.352° · 62.991°
HTM-20 index
-84634903
Similar Worlds
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GJ 180 b
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GJ 887 c
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TOI-4184 b
Sub-Neptune · M-type red dwarf
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GJ 180 c
Sub-Neptune · M-type red dwarf
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GJ 536 b
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Radius 2.41 R⊕ · 34.0 ly