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Rare exoplanet 41 EP

HD 101581 b

RA 175.2563° · Dec -44.4041° · exoplanet

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Score breakdown

· 5 badges
41 pts · Rare
Rare 50 pts → Epic
  • Earth-sized +16
  • Tidally locked +10
  • Multi-planet system +6
  • Confirmed exoplanet +5
  • Found by TESS +4
Total score 41

9 more points to reach Epic.

Badges

  • Confirmed exoplanet · +5
  • Earth-sized · +16
  • Tidally locked · +10
  • Multi-planet system · +6
  • Found by TESS · +4

Trivia

What makes it special

  • Earth-sized. Genuinely comparable to Earth in size. Worlds in this narrow band are the ones every next-generation telescope is being pointed at.

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.
  • Crowded system. One of at least 2 planets orbiting its star.

Sense of scale

  • In perspective. Inside our stellar backyard: every radio broadcast humanity has ever made has already swept past it.

Find it in the sky

  • How to spot it. At magnitude 7.8 it is just past naked-eye reach — ordinary binoculars will pull it in.
  • 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 March — that's when to go looking.

Properties

density gcc
5.2
diameter km
12194.9272
discovery facility
Transiting Exoplanet Survey Satellite (TESS)
discovery method
Transit
discovery year
2025
dist ly
41.6765
eq temp k
834
host star teff
4675
inclination
87.78
insolation
80
mag
7.77
mass earth
0.827
name
HD 101581 b
orbital period days
4.4657
radius earth
0.956
semi major au
0.046
spect
K4/5V
sys num planets
2
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About HD 101581 b

HD 101581 b is a rare exoplanet. It lies about 41.7 light-years from Earth, shines at apparent magnitude 7.77, has spectral type K4/5V and has an equilibrium temperature near 834 K.

Genuinely comparable to Earth in size. Worlds in this narrow band are the ones every next-generation telescope is being pointed at.

How to see it

At apparent magnitude 7.77, it is an easy target for binoculars.

Like any astronomical target, HD 101581 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 HD 101581 b is a rare exoplanet

HD 101581 b scores 41 points on Spacedle's rarity scale, which places it in the rare tier. Another 9 points would lift it into a rarer tier.

That score comes from 5 science badges — Confirmed exoplanet, Earth-sized, Tidally locked, Multi-planet system 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.