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Entering orbit…
Habitability
0/ 100
Uninhabitable
Kepler-42 d rendered in TerraForge from its measured mass, orbit and star

Kepler-42 d

Also written Kepler-42d, Kepler 42d, Kepler 42 d

Rocky Terrestrial131 light years awayFound 2011
Mass
0.36 × Earth
Radius
0.57 × Earth
Gravity
1.10 g
Surface (est.)
496 K
Year
44.9 hrs
From Earth
131 ly
Mass
0.36 × Earth
Radius
0.57 × Earth
Gravity
1.10 g
Surface (est.)
496 K
Year
44.9 hrs
From Earth
131 ly

Kepler-42 system

Type
M-type (Red Dwarf)
Spectral type
M
Temperature
3,068 K
Radius
0.17 ☉
Mass
0.13 ☉
Planets
3
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.

Kepler-42 c0.006 AU60 M⊕
Kepler-42 b0.012 AU0.7 M⊕
Kepler-42 d0.015 AUYou are here0.4 M⊕
Habitable zone

Star and planets drawn to scale: the star is 33 times as wide as Kepler-42 d, so only its edge is in view. Orbits spaced as in the star system view.

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.

Surface. Rocky surface with impact craters, possible volcanic features

Rocky Terrestrial
Low Activity
Kepler-42 d 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)

Reading Kepler-42 d’s atmosphere

Dominant elements: Si, Fe, Mg, Ni, S, AlThis is what a telescope would measure while Kepler-42 d 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-42 d sits about 131 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.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.
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
temperature10
Extremely hot - hostile to known life forms
atmosphere10

Minimal or none

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

Time Dilation

Clocks run 9.1 seconds per year slower than deep space — about 12 minutes over a lifetime

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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