Key parameters at a glance
- A radius of 1.98 Earth radii
- A mass of 5.30 Earth masses
- Surface gravity around 1.35 g
- An orbital period of 1.543 days
- Semi-major axis 0.0195 AU
- Equilibrium temperature 794 K (521 °C)
- Distance from Earth 198.77 light-years
- Earth Similarity Index 0.354
- Travel time at Voyager 1 speed 3,505,267 years
- Almost certainly tidally locked to its host star given the close orbit
TOI-521 b Planet Profile
Physical Specs
Classification
Planet Type
Super-Earth
Discovery
Size rank in cohort
Rank by radius
#25of 1176
top 2.0%
This planet
1.98R⊕
Super-Earth median
1.60R⊕
Nearest-size peers
| Metric | Earth | TOI-521 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 1.98 | 11.21 |
| Mass (M⊕) | 1.00 | 5.30 | 317.83 |
| Density (g/cm³) | 5.51 | 3.80 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.35 | 2.53 |
| Insolation (S⊕) | 1.00 | 66.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 5.300 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 27649847
Gaia DR2
Gaia DR2 649852779797683968
Gaia DR3
Gaia DR3 649852779797683968
System
TOI-521
Percentile among Super-Earth 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 0.0195 AU.
Transit Fingerprint
Depth
0.215 %
Duration
1.180 h
Impact parameter b
0.240
Rp / R★
0.043100
Transit midpoint (BJD)
2,458,492.7153
Photometric dip
Transit produces a flux drop of 2,155 ppm lasting ≈ 1.18 h.
Extended Orbital Architecture
Planet / star radius ratio
0.043100
Semi-major axis / stellar radius
10.100
Impact parameter (b)
0.240
RV semi-amplitude (K)
5.260 m/s
Transit mid-time (BJD)
2,458,492.7153
Long. of periastron (ω)
90.00°
Angular separation (arcsec)
0.32000
Eq. Temperature
794K
(521 °C)
Insolation (S⊕)
66.00
Earth = 1.00
Earth Similarity (ESI)
0.354
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. 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
Lacedelli et al. 2025Instrument
TESS CCD Array
Publication
2025-09
Observation locale
Space
Discovery cohort
Planets confirmed in 2025 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
Host System: TOI-521
Spectral Class
M-type red dwarf
Effective Temperature
3,544 K — cooler than the Sun (5,778 K)
Estimated Age
0.80 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
0.421 R☉
Stellar Mass
0.420 M☉
Metallicity [Fe/H]
-0.12
Extended Stellar Properties
Surface gravity (log g)
4.970 dex
Stellar density
8.177 g/cm³
Systemic radial velocity
-9.31 km/s
Activity index (log R'HK)
-5.500
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
16.380 mas
Total Proper Motion
121.183 mas/yr
PM Right Ascension
90.41 mas/yr
PM Declination
80.69 mas/yr
Galactic Cartesian (pc)
x = -0.537 · y = 0.816 · z = 0.212
Equatorial (J2000)
RA 123.34426° · Dec 12.22211°
Galactic ℓ, b
210.902° · 23.636°
Ecliptic λ, β
122.806° · -7.500°
HTM-20 index
537190698
Similar Worlds
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