Key parameters at a glance
- A radius of 11.99 Earth radii
- A mass of 95.35 Earth masses
- Surface gravity around 0.66 g
- An orbital period of 4.322 days
- Semi-major axis 0.0520 AU
- Equilibrium temperature 1,333 K (1060 °C)
- Distance from Earth 842.87 light-years
- Earth Similarity Index 0.089
- Travel time at Voyager 1 speed 14,864,045 years
WASP-21 b Planet Profile
Physical Specs
Classification
Planet Type
Gas Giant
Discovery
Size rank in cohort
Rank by radius
#1517of 1771
top 85.6%
This planet
11.99R⊕
Gas Giant median
13.52R⊕
Nearest-size peers
| Metric | Earth | WASP-21 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 11.99 | 11.21 |
| Mass (M⊕) | 1.00 | 95.35 | 317.83 |
| Density (g/cm³) | 5.51 | 0.32 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.66 | 2.53 |
| Insolation (S⊕) | 1.00 | 705.04 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 95.345 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 436478932
Gaia DR2
Gaia DR2 2831084391023184128
Gaia DR3
Gaia DR3 2831084391023184128
System
WASP-21
Percentile among Gas Giant cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 4.32 Earth days (1.2% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0520 AU.
Transit Fingerprint
Depth
1.082 %
Duration
3.355 h
Impact parameter b
0.230
Rp / R★
0.103000
Transit midpoint (BJD)
2,454,743.0419
Photometric dip
Transit produces a flux drop of 10,820 ppm lasting ≈ 3.36 h.
Extended Orbital Architecture
Planet / star radius ratio
0.103000
Semi-major axis / stellar radius
10.540
Impact parameter (b)
0.230
RV semi-amplitude (K)
37.200 m/s
Transit mid-time (BJD)
2,454,743.0419
Angular separation (arcsec)
0.20100
Eq. Temperature
1,333K
(1060 °C)
Insolation (S⊕)
705.04
Earth = 1.00
Earth Similarity (ESI)
0.089
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
Bouchy et al. 2010Instrument
iKon-L CCD Camera
Publication
2010-09
Observation locale
Ground
Discovery cohort
Planets confirmed in 2010 at SuperWASP (12 shown).
Host System: WASP-21
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,800 K — hotter than the Sun (5,778 K)
Estimated Age
12.00 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.060 R☉
Stellar Mass
1.010 M☉
Metallicity [Fe/H]
-0.22
Extended Stellar Properties
Surface gravity (log g)
4.277 dex
Stellar density
0.856 g/cm³
Systemic radial velocity
-89.45 km/s
Rotational v·sin i
1.50 km/s
Metallicity ratio
[M/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
3.841 mas
Total Proper Motion
25.800 mas/yr
PM Right Ascension
17.60 mas/yr
PM Declination
18.87 mas/yr
Galactic Cartesian (pc)
x = 0.926 · y = -0.205 · z = 0.316
Equatorial (J2000)
RA 347.49280° · Dec 18.39616°
Galactic ℓ, b
91.754° · -38.256°
Ecliptic λ, β
356.105° · 21.795°
HTM-20 index
1108215053
Observation Record
RV measurements
4
Transmission spectra
2
Emission spectra
2
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