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Entering orbit…
Habitability
0/ 100
Uninhabitable

Kepler-121 b

Lava WorldUninhabitable1666 light years awayFound 2014

Kepler-121 b, from the NASA Exoplanet Archive (found 2014). Measured: 6.08 Earth masses, 0.039 AU, a 5311 K G-type star. Composition inferred from a measured bulk density of 0.47x Earth's — too light for bare rock, so a large fraction of water and ice, with a day locked to its 3.2-day year, as anything orbiting this close would be.

Host star

Kepler-121

Type
G-type (Yellow (Sun-like))
Temperature
5,311 K
Radius
0.701 ☉
Mass
0.859 ☉
Known planets
2, including this one
Luminosity
0.336 ☉

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.

Lava World

Magnetic FieldExtreme Activity
Why is this a Lava World?Your planet's proximity to its star (0.04 AU) results in extreme surface temperatures of 1151K.
Lava worlds orbit so close to their stars that rocky surfaces melt into oceans of molten rock. Recent planet formation can also create temporary lava worlds.
Classification Criteria:
✓ Temperature: 1151K (>1000K)
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.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.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.
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Habitability ScoreUninhabitable
0
Contributing Factors
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere40
Atmosphere present but composition not ideal for life
water15
Abundant water - boiling away, little would be retained
magnetic Field100
Magnetic field provides radiation protection
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
6.08x Earth (3.63e+25 kg)
Radius
1.83x Earth (11,628 km)
This planet: 1.83× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.83x Earth (17.9 m/s²)
Surface Temperature
1,151 K (878 °C / 1,613 °F)
Rotation Period
76.3 hours/day (slower than Earth)
This planet: 76 h/dayEarth: 24 h/day

Orbital Environment

Star Type
G-type (Yellow (Sun-like))
Distance from Star
0.04 AU (5.83 million km)
Orbital Period
3 days
Time Dilation
Clocks run 12.0 seconds per year slower than deep space — about 16 minutes over a lifetime

Atmosphere

Vaporized rock and metals

Elemental Composition

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

Surface Characteristics

Molten surface with lava flows, volcanic activity everywhere
The TerraForge exoplanet catalog: 5,572 real exoplanets run through the simulation, with a search field and rendered worlds grouped by type

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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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