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Rare exoplanet 42 EP

K2-138 e

RA 348.9490° · Dec -10.8497° · exoplanet

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Score breakdown

· 5 badges
42 pts · Rare
Rare 50 pts → Epic
  • Richly packed system +14
  • Tidally locked +10
  • Orbits a Sun-like star +8
  • Confirmed exoplanet +5
  • Sub-Neptune +5
Total score 42

8 more points to reach Epic.

Badges

  • Confirmed exoplanet · +5
  • Sub-Neptune · +5
  • Tidally locked · +10
  • Richly packed system · +14
  • Orbits a Sun-like star · +8

Trivia

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. Too light to be solid rock and too heavy to be all gas: most likely a deep global ocean or a thick steamy envelope over a rocky core.
  • 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.

Could we get there?

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

Properties

density gcc
1.8
diameter km
43243.518
discovery facility
K2
discovery method
Transit
discovery year
2017
dist ly
660.7431
eccentricity
0.077
eq temp k
757
host star teff
5356.3
inclination
88.6
insolation
91.1
mag
12.246
mass earth
12.97
name
K2-138 e
orbital period days
8.2615
radius earth
3.39
semi major au
0.0782
spect
G8 V
sys num planets
6
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About K2-138 e

K2-138 e is a rare 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 757 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 e 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 e is a rare exoplanet

K2-138 e scores 42 points on Spacedle's rarity scale, which places it in the rare tier. Another 8 points would lift it into a rarer tier.

That score comes from 5 science badges — Confirmed exoplanet, Sub-Neptune, Tidally locked, 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.