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Uncommon exoplanet 29 EP

K2-398 c

RA 161.7350° · Dec 1.9367° · exoplanet

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Score breakdown

· 5 badges
29 pts · Uncommon
Uncommon 34 pts → Rare
  • Orbits a Sun-like star +8
  • Distant (over 1,000 light-years) +6
  • Multi-planet system +6
  • Confirmed exoplanet +5
  • Neptune-like +4
Total score 29

5 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Distant (over 1,000 light-years) · +6
  • Neptune-like · +4
  • Multi-planet system · +6
  • 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 2 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 13.3 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.

Properties

density gcc
0.946
diameter km
65031.1076
discovery facility
K2
discovery method
Transit
discovery year
2022
dist ly
1979.7408
host star teff
5946
mag
13.287
mass earth
22.8
name
K2-398 c
orbital period days
18.7878
radius earth
5.098
spect
G2
sys num planets
2
sys num stars
1

About K2-398 c

K2-398 c is an uncommon exoplanet. It lies about 1,979.7 light-years from Earth, shines at apparent magnitude 13.29, has spectral type G2 and spans roughly 5.1 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 13.29, it takes a larger telescope or a long-exposure image to capture.

Like any astronomical target, K2-398 c 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 K2-398 c is an uncommon exoplanet

K2-398 c scores 29 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 5 points would lift it into a rarer tier.

That score comes from 5 science badges — Confirmed exoplanet, Distant (over 1,000 light-years), Neptune-like, Multi-planet 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.