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Entering orbit…
Habitability
5/ 100
Uninhabitable

K2-257 b

Rocky TerrestrialUninhabitable209 light years awayFound 2018

K2-257 b, from the NASA Exoplanet Archive (found 2018). Measured: 0.498 Earth masses, 0.0216 AU, a 3725 K K-type star. Composition inferred from a measured bulk density of 0.87x Earth's, which is rock and iron, with a day locked to its 1.6-day year, as anything orbiting this close would be.

Host star

K2-257

Type
K-type (Orange)
Temperature
3,725 K
Radius
0.5 ☉
Mass
0.52 ☉
Known planets
1 (this one)
Luminosity
0.0416 ☉

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

Low 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: 0.5x 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
5
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere10
No atmosphere - exposed to radiation and temperature extremes
water8
Limited water content - boiling away, little would be retained
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
0.50x Earth (2.97e+24 kg)
Radius
0.79x Earth (5,050 km)
This planet: 0.79× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.79x Earth (7.8 m/s²)
Surface Temperature
854 K (581 °C / 1,078 °F)
Rotation Period
38.6 hours/day (slower than Earth)
This planet: 39 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
0.02 AU (3.23 million km)
Orbital Period
1 day
Time Dilation
Clocks run 15.1 seconds per year slower than deep space — about 20 minutes over a lifetime

Atmosphere

Minimal or none

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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