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Uncommon exoplanet 23 EP

TOI-4666 b

RA 56.2899° · Dec -39.0632° · exoplanet

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Score breakdown

· 4 badges
23 pts · Uncommon
Uncommon 34 pts → Rare
  • Tidally locked +10
  • Confirmed exoplanet +5
  • Gas giant +4
  • Found by TESS +4
Total score 23

11 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Gas giant · +4
  • Tidally locked · +10
  • Found by TESS · +4

Trivia

Hard to believe

  • It would float. It is less dense than water. Drop it in a big enough ocean and the whole world would bob on the surface.

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. Lighter than Neptune — a puffed-up ball of hydrogen and helium with no surface anywhere on it to stand on.

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 15.3 it is far too faint for the eye: this one belongs to cameras and long exposures.
  • Southern sky. It rides the southern half of the sky — an easier target the further south you are.
  • Best time of year. It stands highest in the middle of the night around November — that's when to go looking.

Could we get there?

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

Properties

density gcc
0.43
diameter km
159856.1115
discovery facility
Transiting Exoplanet Survey Satellite (TESS)
discovery method
Transit
discovery year
2025
dist ly
504.7231
eccentricity
0.023
eq temp k
695
host star teff
3793
inclination
89.79
insolation
55.6
mag
15.333
mass earth
155.4181
name
TOI-4666 b
orbital period days
2.9089
radius earth
12.5316
semi major au
0.034
spect
M2±0.5
sys num planets
1
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About TOI-4666 b

TOI-4666 b is an uncommon exoplanet. It lies about 504.7 light-years from Earth, shines at apparent magnitude 15.33, has spectral type M2±0.5 and has an equilibrium temperature near 695 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 15.33, it takes a larger telescope or a long-exposure image to capture.

Like any astronomical target, TOI-4666 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-4666 b is an uncommon exoplanet

TOI-4666 b scores 23 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 11 points would lift it into a rarer tier.

That score comes from 4 science badges — Confirmed exoplanet, Gas giant, 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.