Key parameters at a glance
- A radius of 14.91 Earth radii
- A mass of 750.08 Earth masses
- Surface gravity around 3.37 g
- An orbital period of 1.543 days
- Semi-major axis 0.0236 AU
- Equilibrium temperature 1,357 K (1084 °C)
- Distance from Earth 1,933.75 light-years
- Earth Similarity Index 0.103
- Travel time at Voyager 1 speed 34,101,672 years
- Almost certainly tidally locked to its host star given the close orbit
NGTS-21 b Planet Profile
Physical Specs
Classification
Planet Type
Gas Giant
Discovery
Size rank in cohort
Rank by radius
#242of 1771
top 13.6%
This planet
14.91R⊕
Gas Giant median
13.52R⊕
Nearest-size peers
| Metric | Earth | NGTS-21 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 14.91 | 11.21 |
| Mass (M⊕) | 1.00 | 750.08 | 317.83 |
| Density (g/cm³) | 5.51 | 1.25 | 1.33 |
| Surface Gravity (g) | 1.00 | 3.37 | 2.53 |
| Insolation (S⊕) | 1.00 | 514.29 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 750.075 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 441422655
Gaia DR2
Gaia DR2 6779308394419726848
Gaia DR3
Gaia DR3 6779308394419726848
System
NGTS-21
Percentile among Gas Giant cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 1.54 Earth days (0.4% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0236 AU.
Transit Fingerprint
Depth
2.547 %
Duration
1.950 h
Impact parameter b
0.630
Rp / R★
0.159000
Transit midpoint (BJD)
2,458,228.7785
Photometric dip
Transit produces a flux drop of 25,466 ppm lasting ≈ 1.95 h.
Extended Orbital Architecture
Planet / star radius ratio
0.159000
Semi-major axis / stellar radius
5.890
Impact parameter (b)
0.630
RV semi-amplitude (K)
506.000 m/s
Transit mid-time (BJD)
2,458,228.7785
Long. of periastron (ω)
90.00°
Angular separation (arcsec)
0.03980
Eq. Temperature
1,357K
(1084 °C)
Insolation (S⊕)
514.29
Earth = 1.00
Earth Similarity (ESI)
0.103
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched. Close-orbiting tidally-locked around a cool host.
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
Alves et al. 2022Instrument
NGTS CCD array
Publication
2022-10
Observation locale
Ground
Discovery cohort
Planets confirmed in 2022 at Next-Generation Transit Survey (NGTS) (3 shown).
Host System: NGTS-21
Spectral Class
K-type orange
Effective Temperature
4,660 K — cooler than the Sun (5,778 K)
Estimated Age
10.02 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
0.860 R☉
Stellar Mass
0.720 M☉
Metallicity [Fe/H]
-0.26
Extended Stellar Properties
Surface gravity (log g)
4.630 dex
Stellar density
1.620 g/cm³
Systemic radial velocity
13.75 km/s
Rotation period
17.89 days
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
1.659 mas
Total Proper Motion
15.486 mas/yr
PM Right Ascension
-13.39 mas/yr
PM Declination
-7.78 mas/yr
Galactic Cartesian (pc)
x = 0.537 · y = -0.613 · z = -0.580
Equatorial (J2000)
RA 311.25831° · Dec -35.42784°
Galactic ℓ, b
7.608° · -37.534°
Ecliptic λ, β
304.132° · -16.749°
HTM-20 index
-1495559147
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