← Back to dex
Uncommon exoplanet 31 EP

HD 219666 b

RA 349.5593° · Dec -56.9040° · exoplanet

Loading sky survey…
🌌 View in 3D star map
Tonight’s visibility

Computing the sky for your location…

Score breakdown

· 5 badges
31 pts · Uncommon
Uncommon 34 pts → Rare
  • Tidally locked +10
  • Orbits a Sun-like star +8
  • Confirmed exoplanet +5
  • Neptune-like +4
  • Found by TESS +4
Total score 31

3 more points to reach Rare.

Badges

  • Confirmed exoplanet · +5
  • Neptune-like · +4
  • Tidally locked · +10
  • Found by TESS · +4
  • 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.

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 9.8 you'll want a small backyard telescope.
  • 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
0.87
diameter km
62479.8676
discovery facility
Transiting Exoplanet Survey Satellite (TESS)
discovery method
Transit
discovery year
2018
dist ly
307.1473
eccentricity
0.05
eq temp k
1076
host star teff
5540
inclination
86.42
insolation
598.4408
mag
9.809
mass earth
17.6
name
HD 219666 b
orbital period days
6.0345
radius earth
4.898
semi major au
0.0636
spect
G5 V
sys num planets
1
sys num stars
1
tidally locked
yes
tidally locked inferred
yes

About HD 219666 b

HD 219666 b is an uncommon exoplanet. It lies about 307.1 light-years from Earth, shines at apparent magnitude 9.81, has spectral type G5 V and has an equilibrium temperature near 1,076 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 9.81, a small backyard telescope will bring it into view.

Like any astronomical target, HD 219666 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 HD 219666 b is an uncommon exoplanet

HD 219666 b scores 31 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 3 points would lift it into a rarer tier.

That score comes from 5 science badges — Confirmed exoplanet, Neptune-like, Tidally locked, Found by TESS 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.