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Uncommon exoplanet 32 EP

K2-138 g

RA 348.9490° · Dec -10.8497° · exoplanet

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Score breakdown

· 4 badges
32 pts · Uncommon
Uncommon 34 pts → Rare
  • Richly packed system +14
  • Orbits a Sun-like star +8
  • Confirmed exoplanet +5
  • Sub-Neptune +5
Total score 32

2 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Sub-Neptune · +5
  • Richly packed system · +14
  • Orbits a Sun-like star · +8

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.
  • Crowded system. One of at least 6 planets orbiting its star.

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 12.2 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 September — that's when to go looking.

Properties

density gcc
0.9
diameter km
38434.4306
discovery facility
K2
discovery method
Transit
discovery year
2021
dist ly
660.7431
eccentricity
0.059
eq temp k
445
host star teff
5356.3
inclination
89.4
insolation
9.29
mag
12.246
mass earth
4.32
name
K2-138 g
orbital period days
41.968
radius earth
3.013
semi major au
0.2311
spect
G8 V
sys num planets
6
sys num stars
1

About K2-138 g

K2-138 g is an uncommon exoplanet. It lies about 660.7 light-years from Earth, shines at apparent magnitude 12.25, has spectral type G8 V and has an equilibrium temperature near 445 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 12.25, it takes a larger telescope or a long-exposure image to capture.

Like any astronomical target, K2-138 g 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 K2-138 g is an uncommon exoplanet

K2-138 g scores 32 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 2 points would lift it into a rarer tier.

That score comes from 4 science badges — Confirmed exoplanet, Sub-Neptune, Richly packed system and Orbits a Sun-like star — 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.