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Common exoplanet 19 EP

K2-121 b

RA 126.9367° · Dec 17.5793° · exoplanet

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Score breakdown

· 3 badges
19 pts · Common
Common 22 pts → Uncommon
  • Tidally locked +10
  • Confirmed exoplanet +5
  • Gas giant +4
Total score 19

3 more points to reach Uncommon.

Badges

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

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 13.2 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.

Properties

density gcc
0.7
diameter km
91334.392
discovery facility
K2
discovery method
Transit
discovery year
2017
dist ly
552.5017
eccentricity
0.22
eq temp k
716
host star teff
4526
inclination
89.0266
insolation
62.5
mag
13.229
mass earth
51
name
K2-121 b
orbital period days
5.1857
radius earth
7.16
semi major au
0.0525
sys num planets
1
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About K2-121 b

K2-121 b is a common exoplanet. It lies about 552.5 light-years from Earth, shines at apparent magnitude 13.23, has an equilibrium temperature near 716 K and spans roughly 7.16 Earth radii.

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

Like any astronomical target, K2-121 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 K2-121 b is a common exoplanet

K2-121 b scores 19 points on Spacedle's rarity scale, which places it in the common tier. Another 3 points would lift it into a rarer tier.

That score comes from 3 science badges — Confirmed exoplanet, Gas giant 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.