Key parameters at a glance
- A radius of 1.64 Earth radii
- A mass of 7.50 Earth masses
- Surface gravity around 2.79 g
- An orbital period of 2.786 days
- Semi-major axis 0.0434 AU
- Equilibrium temperature 2,015 K (1742 °C)
- Distance from Earth 353.95 light-years
- Earth Similarity Index 0.119
- Travel time at Voyager 1 speed 6,241,926 years
Kepler-21 b Planet Profile
Physical Specs
Classification
Planet Type
Super-Earth
Discovery
Size rank in cohort
Rank by radius
#515of 1176
top 43.7%
This planet
1.64R⊕
Super-Earth median
1.60R⊕
Nearest-size peers
| Metric | Earth | Kepler-21 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 1.64 | 11.21 |
| Mass (M⊕) | 1.00 | 7.50 | 317.83 |
| Density (g/cm³) | 5.51 | 9.30 | 1.33 |
| Surface Gravity (g) | 1.00 | 2.79 | 2.53 |
| Insolation (S⊕) | 1.00 | 2,749.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 7.500 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
HD
HD 179070
HIP
HIP 94112
TIC
TIC 121214185
Gaia DR2
Gaia DR2 2099606483621385216
Gaia DR3
Gaia DR3 2099606483621385216
System
Kepler-21
Percentile among Super-Earth cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 2.79 Earth days (0.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0434 AU.
Transit Fingerprint
Depth
0.006 %
Duration
3.483 h
Impact parameter b
0.584
Rp / R★
0.007885
Transit midpoint (BJD)
2,455,093.8372
Photometric dip
Transit produces a flux drop of 62 ppm lasting ≈ 3.48 h.
Extended Orbital Architecture
Planet / star radius ratio
0.007885
Semi-major axis / stellar radius
4.929
Impact parameter (b)
0.584
RV semi-amplitude (K)
2.700 m/s
Transit mid-time (BJD)
2,455,093.8372
Long. of periastron (ω)
-15.00°
Angular separation (arcsec)
0.40000
Eq. Temperature
2,015K
(1742 °C)
Insolation (S⊕)
2,749.00
Earth = 1.00
Earth Similarity (ESI)
0.119
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
Howell et al. 2011Instrument
Kepler CCD Array
Publication
2012-02
Observation locale
Space
Discovery cohort
Planets confirmed in 2012 at Kepler (12 shown).
Host System: Kepler-21
Spectral Class
F-type yellow-white
Effective Temperature
6,305 K — hotter than the Sun (5,778 K)
Estimated Age
2.84 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
1.902 R☉
Stellar Mass
1.408 M☉
Metallicity [Fe/H]
-0.03
Extended Stellar Properties
Surface gravity (log g)
4.026 dex
Stellar density
0.287 g/cm³
Systemic radial velocity
-19.10 km/s
Rotational v·sin i
8.40 km/s
Rotation period
13.42 days
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 14 bands
Astrometric Data
Parallax
9.186 mas
Total Proper Motion
39.980 mas/yr
PM Right Ascension
27.95 mas/yr
PM Declination
28.59 mas/yr
Galactic Cartesian (pc)
x = 0.233 · y = -0.745 · z = 0.625
Equatorial (J2000)
RA 287.36197° · Dec 38.71414°
Galactic ℓ, b
69.856° · 13.337°
Ecliptic λ, β
298.183° · 60.466°
HTM-20 index
-691963739
Similar Worlds
Kepler-508 b
Super-Earth · F-type yellow-white
Radius 1.64 R⊕ · 1,058.8 ly
Kepler-1428 b
Super-Earth · F-type yellow-white
Radius 1.64 R⊕ · 4,991.2 ly
Kepler-365 c
Super-Earth · F-type yellow-white
Radius 1.64 R⊕ · 3,388.7 ly
Kepler-208 b
Super-Earth · F-type yellow-white
Radius 1.63 R⊕ · 2,528.8 ly
Kepler-1106 b
Super-Earth · F-type yellow-white
Radius 1.65 R⊕ · 3,557.4 ly
Kepler-360 b
Super-Earth · F-type yellow-white
Radius 1.65 R⊕ · 2,857.3 ly