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Entering orbit…
Habitability
0/ 100
Uninhabitable

Reading K2-117 b’s atmosphere

Dominant elements: H, O, Si, Fe, N, CThis is what a telescope would measure while K2-117 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.K2-117 b sits about 333 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.

K2-117 b

Lava WorldUninhabitable333 light years awayFound 2017

K2-117 b, from the NASA Exoplanet Archive (found 2017). Measured: 4.78 Earth masses, 0.0189 AU, a 3778 K K-type star. Composition inferred from a measured bulk density of 0.57x Earth's at this size, suggesting roughly 69% water/ice by mass, with a day locked to its 1.3-day year, as anything orbiting this close would be.

Host star

K2-117

Type
K-type (Orange)
Spectral type
M1.0 V
Temperature
3,778 K
Radius
0.51 ☉
Mass
0.54 ☉
Known planets
2, including this one
Luminosity
0.0440 ☉

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

No life — too hot for liquid waterMagnetic FieldExtreme Activity
Why is this a Lava World?Your planet's proximity to its star (0.02 AU) results in extreme surface temperatures of 1009K.
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: 1009K (>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.
As an Amazon Associate I earn from qualifying purchases — if you buy through these links, TerraForge may receive a small commission at no extra cost to you.
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
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
4.78x Earth (2.85e+25 kg)
Radius
1.68x Earth (10,732 km)
This planet: 1.68× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.68x Earth (16.5 m/s²)
Surface Temperature
1,009 K (736 °C / 1,357 °F)
Rotation Period
31.0 hours/day (slower than Earth)
This planet: 31 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
0.02 AU (2.83 million km)
Orbital Period
1 day
Time Dilation
Clocks run 17.3 seconds per year slower than deep space — about 23 minutes over a lifetime

Atmosphere

Vaporized rock and metals

Elemental Composition

H - Hydrogen
42.3%
O - Oxygen
30.4%
Si - Silicon
11.0%

Surface Characteristics

Molten surface with lava flows, volcanic activity everywhere
A binary star system's orrery: two suns close together, a red dashed dead-zone boundary, and a debris trail left by a destroyed world

New: Binary Star Systems 🌀

A system can now orbit two suns. Add a companion star when you build one — close, medium, or wide — and the physics decides what survives: a shared center of mass carves out a dead zone where gravity from both stars tears a world apart, leaving it as debris, and every surviving planet's orbit goes elliptical, moving fastest at closest approach and slowest out at aphelion. Push the separation to wide and the dead zone opens tens of AU across, wide enough to gut a system that would have been stable around one star alone. Stand on a world that made it through and you'll watch two suns cross the sky together.

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