Key parameters at a glance
- A radius of 2.88 Earth radii
- A mass of 450.00 Earth masses
- Surface gravity around 54.25 g
- An orbital period of 20.501 days
- Semi-major axis 0.1640 AU
- Equilibrium temperature 662 K (389 °C)
- Distance from Earth 2,835.07 light-years
- Earth Similarity Index 0.124
- Travel time at Voyager 1 speed 49,996,375 years
- Almost certainly tidally locked to its host star given the close orbit
1 sibling around Kepler-391
Kepler-391 c shares its host star with 1 other confirmed planet. Side-by-side measurements below.
| Planet | Type | Radius (R⊕) | Mass (M⊕) | Period (d) | Eq. T (K) | Year |
|---|---|---|---|---|---|---|
| Kepler-391 b | Sub-Neptune | 2.50 | 1,100.00 | 7.418 | 930 | 2014 |
| Kepler-391 c this | Sub-Neptune | 2.88 | 450.00 | 20.501 | 662 | 2014 |
Kepler-391 c Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#653of 1978
top 33.0%
This planet
2.88R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | Kepler-391 c | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.88 | 11.21 |
| Mass (M⊕) | 1.00 | 450.00 | 317.83 |
| Density (g/cm³) | 5.51 | 400.00 | 1.33 |
| Surface Gravity (g) | 1.00 | 54.25 | 2.53 |
| Insolation (S⊕) | 1.00 | 179.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 450.000 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 290032428
Gaia DR2
Gaia DR2 2133196151531241216
Gaia DR3
Gaia DR3 2133196151531241216
System
Kepler-391
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 20.50 Earth days (5.6% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1640 AU.
Transit Fingerprint
Depth
0.009 %
Duration
10.229 h
Impact parameter b
0.561
Rp / R★
0.009150
Transit midpoint (BJD)
2,455,696.9123
Photometric dip
Transit produces a flux drop of 90 ppm lasting ≈ 10.23 h.
Extended Orbital Architecture
Planet / star radius ratio
0.009150
Semi-major axis / stellar radius
12.230
Impact parameter (b)
0.561
RV semi-amplitude (K)
93.000 m/s
Transit mid-time (BJD)
2,455,696.9123
Long. of periastron (ω)
126.00°
Angular separation (arcsec)
0.18900
Eq. Temperature
662K
(389 °C)
Insolation (S⊕)
179.00
Earth = 1.00
Earth Similarity (ESI)
0.124
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.
Discovery Paper
Primary reference
Rowe et al. 2014Instrument
Kepler CCD Array
Publication
2014-03
Observation locale
Space
Discovery cohort
Planets confirmed in 2014 at Kepler (12 shown).
Host System: Kepler-391
Spectral Class
K-type orange
Effective Temperature
5,038 K — cooler than the Sun (5,778 K)
Estimated Age
4.37 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
2.879 R☉
Stellar Mass
1.270 M☉
Metallicity [Fe/H]
0.04
Extended Stellar Properties
Surface gravity (log g)
3.620 dex
Stellar density
0.082 g/cm³
Systemic radial velocity
21.59 km/s
Rotational v·sin i
2.60 km/s
Activity index (log R'HK)
-5.140
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
1.122 mas
Total Proper Motion
12.788 mas/yr
PM Right Ascension
10.30 mas/yr
PM Declination
7.58 mas/yr
Galactic Cartesian (pc)
x = 0.221 · y = -0.588 · z = 0.778
Equatorial (J2000)
RA 290.62188° · Dec 51.05735°
Galactic ℓ, b
82.499° · 16.206°
Ecliptic λ, β
313.858° · 71.369°
HTM-20 index
224213488
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