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Uncommon exoplanet 27 EP

TOI-521 b

RA 123.3443° · Dec 12.2221° · exoplanet

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Score breakdown

· 4 badges
27 pts · Uncommon
Uncommon 34 pts → Rare
  • Tidally locked +10
  • Super-Earth +8
  • Confirmed exoplanet +5
  • Found by TESS +4
Total score 27

7 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Super-Earth · +8
  • Tidally locked · +10
  • Found by TESS · +4

Trivia

What it actually is

  • Hugging its star. It orbits closer to its star than Mercury does to the Sun, completing a lap in less time than Mercury takes.
  • What it is made of. Its density says rock, though lighter than Earth's mix: probably less iron, or a thick shell of water and ice over the top.

Sense of scale

  • In perspective. Far away by human standards, yet still a local address inside the Milky Way's spiral arms.

Find it in the sky

  • How to spot it. At magnitude 14.7 it is far too faint for the eye: this one belongs to cameras and long exposures.
  • Northern sky. It rides the northern half of the sky — an easier target the further north you are.
  • Best time of year. It stands highest in the middle of the night around January — that's when to go looking.

Could we get there?

  • Verdict. Hopelessly far for any craft humanity can build today.

Getting there

  • Aboard Voyager 1. ≈ 3.5 million years at Voyager 1's speed (17 km/s).

Properties

density gcc
3.8
diameter km
25257.276
discovery facility
Transiting Exoplanet Survey Satellite (TESS)
discovery method
Transit
discovery year
2025
dist ly
198.7676
eccentricity
0
eq temp k
794
host star teff
3544
inclination
88.6
insolation
66
mag
14.691
mass earth
5.3
name
TOI-521 b
orbital period days
1.5429
radius earth
1.98
semi major au
0.0195
spect
M3
sys num planets
1
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About TOI-521 b

TOI-521 b is an uncommon exoplanet. It lies about 198.8 light-years from Earth, shines at apparent magnitude 14.69, has spectral type M3 and has an equilibrium temperature near 794 K.

It orbits closer to its star than Mercury does to the Sun, completing a lap in less time than Mercury takes.

How to see it

At apparent magnitude 14.69, it takes a larger telescope or a long-exposure image to capture.

Like any astronomical target, TOI-521 b is best seen from a dark site away from city lights, and when it is above the horizon depends on your latitude and the time of year. The visibility panel above works out tonight's viewing window for your saved location.

Why TOI-521 b is an uncommon exoplanet

TOI-521 b scores 27 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 7 points would lift it into a rarer tier.

That score comes from 4 science badges — Confirmed exoplanet, Super-Earth, Tidally locked and Found by TESS — each earned for a real, measurable property of the object. Rarity on Spacedle is never random: the more remarkable an object's astrophysics, the more badges it collects, the higher it scores, and the rarer it ranks.