Key parameters at a glance
- A radius of 5.41 Earth radii
- A mass of 25.20 Earth masses
- Surface gravity around 0.86 g
- An orbital period of 6.581 days
- Semi-major axis 0.0660 AU
- Equilibrium temperature 881 K (608 °C)
- Distance from Earth 2,544.85 light-years
- Earth Similarity Index 0.206
- Travel time at Voyager 1 speed 44,878,458 years
- Almost certainly tidally locked to its host star given the close orbit
2 siblings around Kepler-257
Kepler-257 c 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-257 b | Sub-Neptune | 2.61 | 7.32 | 2.383 | 1,237 | 2014 |
| Kepler-257 c this | Neptune-like | 5.41 | 25.20 | 6.581 | 881 | 2014 |
| Kepler-257 d | Neptune-like | 4.95 | 21.70 | 24.665 | 567 | 2014 |
Kepler-257 c Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#326of 574
top 56.6%
This planet
5.41R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | Kepler-257 c | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 5.41 | 11.21 |
| Mass (M⊕) | 1.00 | 25.20 | 317.83 |
| Density (g/cm³) | 5.51 | 0.88 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.86 | 2.53 |
| Insolation (S⊕) | 1.00 | 88.60 | 0.037 |
Star Catalogue Identifiers
TIC
TIC 273132699
Gaia DR2
Gaia DR2 2080246282881778048
Gaia DR3
Gaia DR3 2080246282881778048
System
Kepler-257
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 6.58 Earth days (1.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0660 AU.
Transit Fingerprint
Depth
0.251 %
Duration
3.289 h
Impact parameter b
0.760
Rp / R★
0.044931
Transit midpoint (BJD)
2,455,007.7864
Photometric dip
Transit produces a flux drop of 2,513 ppm lasting ≈ 3.29 h.
Extended Orbital Architecture
Planet / star radius ratio
0.044931
Semi-major axis / stellar radius
16.835
Impact parameter (b)
0.760
Transit mid-time (BJD)
2,455,007.7864
Angular separation (arcsec)
0.08460
Eq. Temperature
881K
(608 °C)
Insolation (S⊕)
88.60
Earth = 1.00
Earth Similarity (ESI)
0.206
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-257
Spectral Class
K-type orange
Effective Temperature
5,180 K — cooler than the Sun (5,778 K)
Estimated Age
1.48 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
1.037 R☉
Stellar Mass
0.916 M☉
Metallicity [Fe/H]
0.40
Extended Stellar Properties
Surface gravity (log g)
4.360 dex
Stellar density
1.630 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
1.254 mas
Total Proper Motion
3.153 mas/yr
PM Right Ascension
3.14 mas/yr
PM Declination
0.30 mas/yr
Galactic Cartesian (pc)
x = 0.319 · y = -0.617 · z = 0.720
Equatorial (J2000)
RA 297.31600° · Dec 46.02326°
Galactic ℓ, b
79.871° · 10.012°
Ecliptic λ, β
318.712° · 64.910°
HTM-20 index
-2132779053
Similar Worlds
Kepler-1737 b
Neptune-like · K-type orange
Radius 5.40 R⊕ · —
HD 99492 b
Neptune-like · K-type orange
Radius 5.44 R⊕ · 59.4 ly
TOI-1694 b
Neptune-like · K-type orange
Radius 5.34 R⊕ · 406.7 ly
Kepler-957 b
Neptune-like · K-type orange
Radius 5.50 R⊕ · 2,689.8 ly
TOI-3568 b
Neptune-like · K-type orange
Radius 5.30 R⊕ · 645.5 ly
HD 192310 c
Neptune-like · K-type orange
Radius 5.25 R⊕ · 28.7 ly