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Common exoplanet 18 EP

HD 128717 b

RA 219.0882° · Dec 57.5610° · exoplanet

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Score breakdown

· 3 badges
18 pts · Common
Common 22 pts → Uncommon
  • Eccentric orbit +9
  • Confirmed exoplanet +5
  • Gas giant +4
Total score 18

4 more points to reach Uncommon.

Badges

  • Confirmed exoplanet · +5
  • Gas giant · +4
  • Eccentric orbit · +9

Trivia

Hard to believe

  • Denser than iron. It is packed tighter than solid iron — whatever it is made of, it is not ordinary rock.

What it actually is

  • What it is made of. Denser than Earth — a solid world of rock and iron, with no meaningful atmosphere to speak of by mass.

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 8.3 it is just past naked-eye reach — ordinary binoculars will pull it in.
  • Northern sky. It rides the northern half of the sky — an easier target the further north you are.
  • Best time of year. It stands highest in the middle of the night around April — that's when to go looking.

Could we get there?

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

Getting there

  • Aboard Voyager 1. ≈ 4.2 million years at Voyager 1's speed (17 km/s).

Properties

density gcc
19.5
diameter km
154350.02
discovery facility
European Space Agency (ESA) Gaia Satellite
discovery method
Astrometry
discovery year
2025
dist ly
240.1682
eccentricity
0.85
eq temp k
151.9
host star teff
6210
inclination
130.3
insolation
0.0892
mag
8.32
mass earth
6293.0025
name
HD 128717 b
orbital period days
3420
radius earth
12.1
semi major au
4.85
sys num planets
1
sys num stars
1

About HD 128717 b

HD 128717 b is a common exoplanet. It lies about 240.2 light-years from Earth, shines at apparent magnitude 8.32, has an equilibrium temperature near 152 K and spans roughly 12.1 Earth radii.

Denser than Earth — a solid world of rock and iron, with no meaningful atmosphere to speak of by mass.

How to see it

At apparent magnitude 8.32, it is an easy target for binoculars.

Like any astronomical target, HD 128717 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 128717 b is a common exoplanet

HD 128717 b scores 18 points on Spacedle's rarity scale, which places it in the common tier. Another 4 points would lift it into a rarer tier.

That score comes from 3 science badges — Confirmed exoplanet, Gas giant and Eccentric orbit — 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.