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Entering orbit…
Habitability
25/ 100
Extremely Harsh

YZ Cet b

Rocky TerrestrialExtremely Harsh12 light years awayFound 2017

YZ Cet b, from the NASA Exoplanet Archive (found 2017). Measured: 0.7 Earth masses, 0.0163 AU, a 3151 K M-type star. Composition inferred from a measured bulk density of 0.92x Earth's, which is rock and iron, with a day locked to its 2.0-day year, as anything orbiting this close would be.

Host star

YZ Cet

Type
M-type (Red Dwarf)
Spectral type
M4.5 V
Temperature
3,151 K
Radius
0.157 ☉
Mass
0.142 ☉
Known planets
3, including this one
Luminosity
2.19e-3 ☉

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.

Rocky Terrestrial

Magnetic FieldLow Activity
Why is this a Rocky Terrestrial?Your planet is dominated by silicate (25.0%) and iron (12.5%) content, forming a rocky terrestrial body.
Rocky terrestrial planets are primarily composed of silicate rocks and metals. They're the most common type of small planet in the universe.
Classification Criteria:
✓ Silicon: 25.0% + Iron: 12.5% + Magnesium: 3.8%✓ Mass: 0.7x Earth (terrestrial range)
Further reading
The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.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
25
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere70
Nitrogen atmosphere provides protection but not breathable
water31
Limited water content - likely as steam (low gravity lets water escape to space)
magnetic Field100
Magnetic field provides radiation protection
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
0.70x Earth (4.18e+24 kg)
Radius
0.89x Earth (5,657 km)
This planet: 0.89× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.89x Earth (8.7 m/s²)
Surface Temperature
477 K (204 °C / 399 °F)
Rotation Period
48.5 hours/day (slower than Earth)
This planet: 48 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.02 AU (2.44 million km)
Orbital Period
1 day
Time Dilation
Clocks run 8.6 seconds per year slower than deep space — about 11 minutes over a lifetime

Atmosphere

Thin CO₂ and nitrogen atmosphere

Elemental Composition

O - Oxygen
31.3%
Si - Silicon
25.0%
Fe - Iron
12.5%

Surface Characteristics

Rocky surface with impact craters, possible volcanic features
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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