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Entering orbit…
Habitability
9/ 100
Uninhabitable

GJ 3138 b

Rocky TerrestrialUninhabitable93 light years awayFound 2017

GJ 3138 b, from the NASA Exoplanet Archive (found 2017). Measured: 1.78 Earth masses, 0.0197 AU, a 3717 K K-type star. Composition inferred from a measured bulk density of 1.08x Earth's, which is rock and iron, with a day locked to its 1.2-day year, as anything orbiting this close would be.

Host star

GJ 3138

Type
K-type (Orange)
Spectral type
M0
Temperature
3,717 K
Radius
0.5 ☉
Mass
0.681 ☉
Known planets
3, including this one
Luminosity
0.0450 ☉

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 FieldModerate 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: 1.8x 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 ScoreUninhabitable
9
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere70
Nitrogen atmosphere provides protection but not breathable
water8
Limited water content - boiling away, little would be retained
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
1.78x Earth (1.06e+25 kg)
Radius
1.21x Earth (7,721 km)
This planet: 1.21× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.21x Earth (11.9 m/s²)
Surface Temperature
926 K (652 °C / 1,206 °F)
Rotation Period
29.3 hours/day (slower than Earth)
This planet: 29 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
0.02 AU (2.95 million km)
Orbital Period
1 day
Time Dilation
Clocks run 16.6 seconds per year slower than deep space — about 22 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
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