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Entering orbit…
Habitability
21/ 100
Extremely Harsh

Kapteyn c

Ice GiantExtremely Harsh13 light years awayFound 2014

Kapteyn c, from the NASA Exoplanet Archive (found 2014). Measured: 7 Earth masses, 0.311 AU, a 3550 K M-type star. Composition inferred from a measured bulk density of 0.43x Earth's — too light for bare rock, so a large fraction of water and ice, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

Kapteyn

Type
M-type (Red Dwarf)
Spectral type
M2.0V
Temperature
3,550 K
Radius
0.291 ☉
Mass
0.281 ☉
Known planets
1 (this one)
Luminosity
0.0161 ☉

Published by the NASA Exoplanet Archive. This world’s temperature and habitability score are computed from this star’s measured luminosity, not from a stand-in for its class.

Ice Giant

Magnetic FieldModerate Activity
Why is this a Ice Giant?Your planet has moderate mass (7.0x Earth) with significant water, carbon, and nitrogen content, characteristic of ice giants.
Ice giants like Uranus and Neptune have icy interiors with thick atmospheres of hydrogen and helium, but not enough to be classified as gas giants.
Classification Criteria:
✓ Mass: 7.0x Earth (5-20x range)✓ Water/Carbon/Nitrogen rich composition
Further reading
Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.Envisioning ExoplanetsMichael CarrollWhat these worlds might look like from the ground, painted from the same measurements this page renders.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.
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Habitability ScoreExtremely Harsh
21
Contributing Factors
temperature20
Very cold - water frozen, challenging for life
atmosphere30
Hydrogen-rich atmosphere typical of gas giants
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
7.00x Earth (4.18e+25 kg)
Radius
1.91x Earth (12,187 km)
This planet: 1.91× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.91x Earth (18.8 m/s²)
Surface Temperature
191 K (-82 °C / -116 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.31 AU (46.5 million km)
Orbital Period
116 days

Atmosphere

Hydrogen and helium with water, methane, and ammonia ices

Elemental Composition

O - Oxygen
41.2%
H - Hydrogen
17.6%
Si - Silicon
11.8%

Surface Characteristics

Icy mantle surrounding rocky core, with hydrogen-helium atmosphere
The TerraForge exoplanet catalog: 5,572 real exoplanets run through the simulation, with a search field and rendered worlds grouped by type

New: The Exoplanet Catalog 🔭

Every confirmed planet NASA has measured well enough to build — 5,572 of them — is now in here, and none of them arrived with a label. Their real mass, radius, orbit and star go through the same simulation that runs everything you make, and it decides what each one is: gas giant, lava world, ocean, ice. Sixteen come out Earth-like. Find TRAPPIST-1e, stand on its surface, and see what a red dwarf's light actually looks like from the ground.

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