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Rare exoplanet 46 EP

GJ 3998 d

RA 259.0021° · Dec 11.0562° · exoplanet

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Score breakdown

· 4 badges
46 pts · Rare
Rare 50 pts → Epic
  • In the habitable zone +30
  • Multi-planet system +6
  • Confirmed exoplanet +5
  • Sub-Neptune +5
Total score 46

4 more points to reach Epic.

Badges

  • Confirmed exoplanet · +5
  • In the habitable zone · +30
  • Sub-Neptune · +5
  • Multi-planet system · +6

Trivia

What makes it special

  • Goldilocks zone. Sits where it's neither too hot nor too cold — liquid water could exist on a surface here.

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.
  • What the zone means. The habitable zone is only about temperature: it is the band where liquid water could survive on a surface. It is a promising address, not evidence of anything living.
  • Crowded system. One of at least 3 planets orbiting its star.

Sense of scale

  • In perspective. Inside our stellar backyard: every radio broadcast humanity has ever made has already swept past it.

Find it in the sky

  • How to spot it. At magnitude 10.8 you'll want a small backyard telescope.
  • Northern sky. It rides the northern half of the sky — an easier target the further north you are.

Properties

density gcc
2.6
diameter km
29849.508
discovery facility
Multiple Observatories
discovery method
Radial Velocity
discovery year
2025
dist ly
59.1839
eccentricity
0
eq temp k
292.23
habitable zone
yes
host star teff
3726
insolation
1.2
mag
10.844
mass earth
6.07
name
GJ 3998 d
orbital period days
41.78
radius earth
2.34
semi major au
0.189
spect
M1
sys num planets
3
sys num stars
1

About GJ 3998 d

GJ 3998 d is a rare exoplanet. It lies about 59.2 light-years from Earth, shines at apparent magnitude 10.84, has spectral type M1 and has an equilibrium temperature near 292 K.

Sits where it's neither too hot nor too cold — liquid water could exist on a surface here.

How to see it

At apparent magnitude 10.84, a small backyard telescope will bring it into view.

Like any astronomical target, GJ 3998 d 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 GJ 3998 d is a rare exoplanet

GJ 3998 d scores 46 points on Spacedle's rarity scale, which places it in the rare tier. Another 4 points would lift it into a rarer tier.

That score comes from 4 science badges — Confirmed exoplanet, In the habitable zone, Sub-Neptune and Multi-planet system — 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.