Key parameters at a glance
- A radius of 2.73 Earth radii
- A mass of 3.61 Earth masses
- Surface gravity around 0.48 g
- An orbital period of 10.042 days
- Semi-major axis 0.0870 AU
- Equilibrium temperature 712 K (439 °C)
- Distance from Earth 1,256.45 light-years
- Earth Similarity Index 0.298
- Travel time at Voyager 1 speed 22,157,565 years
3 siblings around Kepler-221
Kepler-221 d shares its host star with 3 other confirmed planets. Side-by-side measurements below.
| Planet | Type | Radius (R⊕) | Mass (M⊕) | Period (d) | Eq. T (K) | Year |
|---|---|---|---|---|---|---|
| Kepler-221 b | Super-Earth | 1.71 | 5.96 | 2.796 | 1,090 | 2014 |
| Kepler-221 c | Sub-Neptune | 2.93 | 9.30 | 5.691 | 860 | 2014 |
| Kepler-221 d this | Sub-Neptune | 2.73 | 3.61 | 10.042 | 712 | 2014 |
| Kepler-221 e | Sub-Neptune | 2.63 | 7.87 | 18.370 | 582 | 2014 |
Kepler-221 d Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#823of 1978
top 41.6%
This planet
2.73R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | Kepler-221 d | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.73 | 11.21 |
| Mass (M⊕) | 1.00 | 3.61 | 317.83 |
| Density (g/cm³) | 5.51 | 0.90 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.48 | 2.53 |
| Insolation (S⊕) | 1.00 | 56.29 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 3.610 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 272601375
Gaia DR2
Gaia DR2 2080344586094498432
Gaia DR3
Gaia DR3 2080344586094498432
System
Kepler-221
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 10.04 Earth days (2.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0870 AU.
Transit Fingerprint
Depth
0.116 %
Duration
2.530 h
Impact parameter b
0.360
Rp / R★
0.030708
Transit midpoint (BJD)
2,454,970.0846
Photometric dip
Transit produces a flux drop of 1,155 ppm lasting ≈ 2.53 h.
Extended Orbital Architecture
Planet / star radius ratio
0.030708
Semi-major axis / stellar radius
30.730
Impact parameter (b)
0.360
Transit mid-time (BJD)
2,454,970.0846
Angular separation (arcsec)
0.22600
Eq. Temperature
712K
(439 °C)
Insolation (S⊕)
56.29
Earth = 1.00
Earth Similarity (ESI)
0.298
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.
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-221
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,243 K — cooler than the Sun (5,778 K)
Estimated Age
1.78 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
0.821 R☉
Stellar Mass
0.854 M☉
Metallicity [Fe/H]
0.06
Extended Stellar Properties
Surface gravity (log g)
4.543 dex
Stellar density
1.800 g/cm³
Metallicity ratio
[M/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
2.567 mas
Total Proper Motion
3.487 mas/yr
PM Right Ascension
-2.71 mas/yr
PM Declination
-2.20 mas/yr
Galactic Cartesian (pc)
x = 0.307 · y = -0.611 · z = 0.729
Equatorial (J2000)
RA 296.65475° · Dec 46.83522°
Galactic ℓ, b
80.373° · 10.802°
Ecliptic λ, β
318.570° · 65.839°
HTM-20 index
-1912311971
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