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Entering orbit…
Habitability
8/ 100
Uninhabitable
Kepler-258 b rendered in TerraForge from its measured mass, orbit and star

Kepler-258 b

Also written Kepler-258b, Kepler 258b, Kepler 258 b

Ice Giant1878 light years awayFound 2014
Mass
15.50 × Earth
Radius
4.06 × Earth
Gravity
0.94 g
Surface (est.)
648 K
Year
13.2 days
From Earth
1,879 ly
Mass
15.50 × Earth
Radius
4.06 × Earth
Gravity
0.94 g
Surface (est.)
648 K
Year
13.2 days
From Earth
1,879 ly

Kepler-258 system

Type
K-type (Orange)
Temperature
4,942 K
Radius
0.915 ☉
Mass
0.82 ☉
Planets
2
Luminosity
0.266 ☉

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.

Kepler-258 b0.10 AUYou are here16 M⊕
Kepler-258 c0.19 AU13 M⊕
Habitable zone

Star and planets drawn to scale: the star is 25 times as wide as Kepler-258 b, so only its edge is in view. Orbits spaced as in the star system view.

Kepler-258 b, from the NASA Exoplanet Archive (found 2014). Measured: 15.5 Earth masses, 0.103 AU, a 4942 K K-type star. Composition inferred from a measured bulk density of 0.23x Earth's, larger than even a pure water/ice world of this mass, suggesting a water-rich interior under roughly a 15% hydrogen/helium envelope by mass, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Surface. No solid surface - a deep volatile envelope over a supercritical water mantle and hot-ice interior

Ice Giant
Magnetic FieldExtreme Activity
Kepler-258 b has moderate mass (15.5x 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: 15.5x Earth (5-20x range)✓ Water/Carbon/Nitrogen rich composition

Reading Kepler-258 b’s atmosphere

Dominant elements: H, O, Si, He, Fe, NThis is what a telescope would measure while Kepler-258 b crosses in front of its star: starlight passes through the atmosphere and spreads into a rainbow band. Each dark line marks a wavelength the atmosphere absorbed.Every element absorbs its own signature wavelengths — hydrogen always darkens the same two spots, calcium another pair, and so on. Astronomers match the lines in a real spectrum against a library of these signatures to say what an atmosphere is made of, light-years away, without ever visiting. A deeper line generally means more of that element is present.Kepler-258 b sits about 1879 light-years away, found by the transit method. Most catalogued distances trace back to parallax: as Earth orbits the Sun, a nearby star appears to shift very slightly against the distant background stars, and the size of that shift gives its distance directly.
Further reading
ExoplanetsSara Seager (editor)The field's standard reference: how planets are found, how they form, and what their atmospheres are made of.The Planet FactoryElizabeth TaskerHow planets are made, and why so few of them come out like Earth.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.
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Habitability ScoreUninhabitable
8
Contributing Factors
temperature4
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere30

Hydrogen and helium with water, methane, and ammonia ices

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
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
15.50x Earth (9.26e+25 kg)
Radius
2.49x Earth (15,885 km)
This planet: 2.49× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.49x Earth (24.5 m/s²)
Surface Temperature
648 K (375 °C / 708 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Elemental Composition

A dark ringed planet hanging over the horizon of a rocky moon, its rings lit by a distant sun

New: Stand on Your Moons 🌒

A planet's surface view isn't the only ground any more. Press the surface button on a planet with moons and it asks where to stand: the planet itself, or any moon still in orbit, each tagged with what it became — ocean, ice, carbon, volcanic. Every moon gets its own ground and sky from its own physics: airless rock under a black sky, ice cracked by geysers over a hidden sea, sulfur plains shaking with eruptions, or orange haze you can't see the sun through. And hanging over the horizon, there's the planet you built.

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