Temperature
4043 K
4006 to 4222.1
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Stellar HostProfile
K2-21
M0.0 โข 83.64 pc
Records
9
literature rows
Planets
2
system count
References
9
distinct source labels
TIC: TIC 240766850
Approximate color
from effective temperature
Canonical Summary
Adopted host values from one source row
Values come from the row with the most populated summary measurements. Missing values stay missing. Ranges and counts describe all source rows.
Stellar source: Petigura et al. 2015 โข System source: TICv8
Mass
0.64 Msun
0.52 to 0.68
Radius
0.60 Rsun
0.46 to 0.65
Age
1 Gyr
single adopted value
Distance
83.64 pc
single adopted value
Spectral Type
M0.0
Consistent across records
Planets
2
Stable across source rows
Scale Comparison
Radius against the Sun
Current adopted radius: 0.60 Rโ (circles scaled linearly by radius)
Sun
1.0 Rโ baseline
K2-21
0.60 Rโ
System Layout
Known planets
2 planets linked to this host
K2-21 and Its Two Super-Earths
K2-21 is an M0.0 star located 273 light-years away. Its reported mass estimate is 0.64 solar masses and its reported radius estimate is 0.6 solar radii, both smaller than the Sun's. Its reported temperature is 4040 K, cooler than the Sun's, and it has a reported lower limit of 1 billion years. The star hosts two planets, both discovered in 2015 by the transit method, which detects the small dip in brightness caused when a planet crosses in front of its star from our viewpoint.
Both planets are Super-Earths, a size class for planets reaching up to 2.5 times Earth's radius. K2-21 b has a reported radius estimate of 1.84 Earth radii, larger than Earth's, while K2-21 c has a reported radius estimate of 2.49 Earth radii, also larger than Earth's. Among the listed planets, K2-21 b has the smallest radius and K2-21 c the largest.
The two planets differ in their years. K2-21 b completes one orbit in 9.33 days, and K2-21 c in 15.5 days. Among the listed planets, K2-21 b has the shortest year by reported estimates and K2-21 c the longest.
Provenance
Underlying measurements and references
Evidence Summary
Rows
9
Stellar refs
8
System refs
1
Distancestable
Parallaxstable
Temperaturedisputed
Massdisputed
Radiusdisputed
Agestable
Luminositydisputed
Surface Gravitydisputed
Metallicitystable
Spectral Typestable
| ST TEFF | ST MASS | ST RAD | ST AGE | ST LUM | ST SPECTYPE | SY DIST | Stellar Ref | System Ref |
|---|---|---|---|---|---|---|---|---|
| 4006 | 0.52 | 0.46 | โ | โ | โ | 83.64 | Crossfield et al. 2016 | TICv8 |
| 4047 | 0.63 | 0.65 | โ | -0.98 | โ | 83.64 | TICv8 | TICv8 |
| 4222.1 | 0.68 | 0.65 | โ | โ | โ | 83.64 | Dressing et al. 2017 | TICv8 |
| 4213.5 | โ | 0.58 | โ | -1.03 | โ | 83.64 | Gaia DR2 | TICv8 |
| 4043 | 0.64 | 0.60 | 1 | โ | M0.0 | 83.64 | Petigura et al. 2015 | TICv8 |
| โ | โ | โ | โ | โ | โ | 83.64 | Barros et al. 2016 | TICv8 |
| โ | โ | 0.58 | โ | โ | โ | 83.64 | Kruse et al. 2019 | TICv8 |
| 4024 | โ | 0.60 | โ | โ | โ | 83.64 | Vanderburg et al. 2016 | TICv8 |
| โ | โ | 0.58 | โ | โ | โ | 83.64 | Kruse et al. 2019 | TICv8 |