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Uncommon exoplanet 31 EP

K2-257 b

RA 188.2783° · Dec -1.9533° · exoplanet

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Score breakdown

· 3 badges
31 pts · Uncommon
Uncommon 34 pts → Rare
  • Earth-sized +16
  • Tidally locked +10
  • Confirmed exoplanet +5
Total score 31

3 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Earth-sized · +16
  • Tidally locked · +10

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.

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 13.7 it is far too faint for the eye: this one belongs to cameras and long exposures.
  • Seen from everywhere. It sits almost on the celestial equator, so it can be seen from essentially anywhere on Earth.
  • Best time of year. It stands highest in the middle of the night around March — that's when to go looking.

Could we get there?

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

Properties

density gcc
4.79
diameter km
10587.646
discovery facility
K2
discovery method
Transit
discovery year
2018
dist ly
208.761
eq temp k
789
host star teff
3725
insolation
89.1463
mag
13.716
mass earth
0.498
name
K2-257 b
orbital period days
1.6059
radius earth
0.83
semi major au
0.0216
sys num planets
1
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About K2-257 b

K2-257 b is an uncommon exoplanet. It lies about 208.8 light-years from Earth, shines at apparent magnitude 13.72, has an equilibrium temperature near 789 K and spans roughly 0.83 Earth radii.

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 13.72, it takes a larger telescope or a long-exposure image to capture.

Like any astronomical target, K2-257 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 K2-257 b is an uncommon exoplanet

K2-257 b scores 31 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 3 points would lift it into a rarer tier.

That score comes from 3 science badges — Confirmed exoplanet, Earth-sized and Tidally locked — 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.