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Entering orbit…
Habitability
18/ 100
Uninhabitable
Kepler-538 Ac rendered in TerraForge from its measured mass, orbit and star

Kepler-538 Ac

Also written Kepler 538 Ac

Rocky Terrestrial509 light years awayFound 2019
Mass
0.24 × Earth
Radius
0.63 × Earth
Gravity
0.61 g
Surface (est.)
374 K
Year
118 days
From Earth
509 ly
Mass
0.24 × Earth
Radius
0.63 × Earth
Gravity
0.61 g
Surface (est.)
374 K
Year
118 days
From Earth
509 ly

Kepler-538 system

Type
G-type (Yellow (Sun-like))
Spectral type
G5V
Temperature
5,534 K
Radius
0.872 ☉
Mass
0.892 ☉
Planets
2
Luminosity
0.642 ☉

Published by the Extrasolar Planets Encyclopaedia. This world’s temperature and habitability score are computed from its star’s published radius and temperature.

Kepler-538 b0.35 AU13 M⊕
Kepler-538 Ac0.45 AUYou are here0.2 M⊕
Habitable zone

Star and planets drawn to scale: the star is 151 times as wide as Kepler-538 Ac, so only its edge is in view. Orbits spaced as in the star system view.

exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

Kepler-538 Ac, from the Extrasolar Planets Encyclopaedia (found 2019). Measured: 0.242 Earth masses, 0.45 AU, a 5534 K G-type star. Composition inferred from a measured bulk density of 0.97x Earth's, which is rock and iron, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Surface. Rocky surface with impact craters, possible volcanic features

Rocky Terrestrial
Life unlikely — too hot for liquid waterNone Activity
Kepler-538 Ac 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: 0.2x Earth (terrestrial range)

Reading Kepler-538 Ac’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while Kepler-538 Ac 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-538 Ac sits about 509 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.
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Habitability ScoreUninhabitable
18
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere70

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable
water25
Limited water content - likely as steam (low gravity lets water escape to space)
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology30
Geologically dead - no nutrient recycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
0.24x Earth (1.45e+24 kg)
Radius
0.62x Earth (3,970 km)
This planet: 0.62× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.62x Earth (6.1 m/s²)
Surface Temperature
374 K (100 °C / 213 °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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