Rare exoplanet 33 EP

HAT-P-21 b

RA 171.2749° · Dec 41.0280° · exoplanet

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Score breakdown

· 4 badges

33 pts · Rare

Rare 46 pts → Epic

Lava world +14
Hot Jupiter +10
Confirmed exoplanet +5
Gas giant +4

Total score 33

13 more points to reach Epic.

Badges

Confirmed exoplanet · +5
Gas giant · +4
Hot Jupiter · +10
Lava world · +14

Trivia

What makes it special

Lava world. Its surface is likely an ocean of molten rock.

Could we get there?

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

Getting there

Aboard Voyager 1. ≈ 15.9 million years at Voyager 1's speed (17 km/s).
Fastest probe ever. ≈ 1.4 million years even at the Parker Solar Probe's 192 km/s.
At 10% light speed. ≈ 9044 years in a starship at a tenth of light speed.
Distance. 904 light-years from Earth.

Look-back time

Look-back time. The light you'd see left around the year 1122.

Saying hello

Say hello. A radio message and its reply would take 1809 years round-trip.

Standing on it

A year here. A full year lasts just 4.1 Earth days.

By the numbers

Size. About 12.4× the width of Earth.
Volume. About 1926 Earths could fit inside it.
Mass. Roughly 1548× Earth's mass — about 4.9 Jupiters.
Your weight. You'd weigh about 10.0× your Earth weight standing here.
Temperature. Around 1094°C — hotter than a self-cleaning oven.

How we found it

Discovery. Found by HATNet using the transit method.

Properties

density gcc: 3.6338
discovery facility: HATNet
discovery method: Transit
dist ly: 904.3588
eccentricity: 0.23
eq temp k: 1367
insolation: 459.542
mass earth: 1547.8321
name: HAT-P-21 b
orbital period days: 4.1245
radius earth: 12.442
sys num planets: 1

About HAT-P-21 b

HAT-P-21 b is a rare exoplanet. It lies about 904.4 light-years from Earth, has an equilibrium temperature near 1,367 K, spans roughly 12.44 Earth radii and weighs about 1,547.83 Earth masses.

Its surface is likely an ocean of molten rock.

How to see it

Like any astronomical target, HAT-P-21 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 HAT-P-21 b is a rare exoplanet

HAT-P-21 b scores 33 points on Spacedle's rarity scale, which places it in the rare tier. Another 13 points would lift it into a rarer tier.

That score comes from 4 science badges — Confirmed exoplanet, Gas giant, Hot Jupiter and Lava world — 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.