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Entering orbit…
Habitability
0/ 100
Uninhabitable

Kepler-42 d

Rocky TerrestrialUninhabitable131 light years awayFound 2011

Kepler-42 d, from the NASA Exoplanet Archive (found 2011). Measured: 0.358 Earth masses, 0.0154 AU, a 3068 K M-type star. Composition inferred from a measured bulk density of 1.93x Earth's, far too high for silicates alone — an iron-rich world, with a day locked to its 1.9-day year, as anything orbiting this close would be.

Host star

Kepler-42

Type
M-type (Red Dwarf)
Spectral type
M
Temperature
3,068 K
Radius
0.17 ☉
Mass
0.13 ☉
Known planets
3, including this one
Luminosity
2.40e-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

Low Activity
Why is this a Rocky Terrestrial?Your planet is dominated by silicate (36.6%) and iron (24.4%) 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: 36.6% + Iron: 24.4% + Magnesium: 12.2%✓ Mass: 0.4x 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
0
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere10
No atmosphere - exposed to radiation and temperature extremes
water0
No water - the recipe has no hydrogen and oxygen to form it
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry20
Limited organic chemistry potential
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
0.36x Earth (2.14e+24 kg)
Radius
0.71x Earth (4,524 km)
This planet: 0.71× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.71x Earth (7.0 m/s²)
Surface Temperature
496 K (223 °C / 433 °F)
Rotation Period
44.9 hours/day (slower than Earth)
This planet: 45 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.02 AU (2.3 million km)
Orbital Period
1 day
Time Dilation
Clocks run 9.1 seconds per year slower than deep space — about 12 minutes over a lifetime

Atmosphere

Minimal or none

Elemental Composition

Si - Silicon
36.6%
Fe - Iron
24.4%
Mg - Magnesium
12.2%

Surface Characteristics

Rocky surface with impact craters, possible volcanic features
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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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