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Entering orbit…
Habitability
6/ 100
Uninhabitable
TOI-1803 c rendered in TerraForge from its measured mass, orbit and star

TOI-1803 c

Also written TOI-1803c, TOI 1803c, TOI 1803 c

Barren388 light years awayFound 2025
Mass
8.00 × Earth
Radius
4.29 × Earth
Gravity
0.43 g
Surface (est.)
634 K
Year
12.9 days
From Earth
388 ly
Mass
8.00 × Earth
Radius
4.29 × Earth
Gravity
0.43 g
Surface (est.)
634 K
Year
12.9 days
From Earth
388 ly

TOI-1803 system

Type
K-type (Orange)
Temperature
4,687 K
Radius
0.715 ☉
Mass
0.756 ☉
Planets
2
Luminosity
0.222 ☉

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.

TOI-1803 b0.060 AU10 M⊕
TOI-1803 c0.097 AUYou are here8.0 M⊕
Habitable zone

Star and planets drawn to scale: the star is 18 times as wide as TOI-1803 c, so only its edge is in view. Orbits spaced as in the star system view.

TOI-1803 c, from the NASA Exoplanet Archive (found 2025). Measured: 8 Earth masses, 0.097 AU, a 4687 K K-type star. Composition inferred from a measured bulk density of 0.10x Earth's, larger than even a pure water/ice world of this mass, suggesting a water-rich interior under roughly a 26% hydrogen/helium envelope by mass, with a day locked to its 12.9-day year, as anything orbiting this close would be.

Surface. Barren rocky surface with unusual elemental composition

Barren
Extreme Activity
TOI-1803 c has an unusual composition that doesn't fit standard classifications, or lacks the elements needed for complex geological processes.
Barren worlds can form from uncommon element combinations or may be remnants of larger bodies that lost their atmospheres and volatile materials.
Classification Criteria:
Composition doesn't match standard planet typesMass: 8.0x EarthTemperature: 634K

Reading TOI-1803 c’s atmosphere

Dominant elements: H, O, He, Si, Fe, NThis is what a telescope would measure while TOI-1803 c 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.TOI-1803 c sits about 388 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
6
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere42

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable (partially stripped by slow rotation)
water15
Abundant water - boiling away, little would be retained
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - days and nights each last several Earth days, bringing extreme temperature swings

Physical Properties

Mass
8.00x Earth (4.78e+25 kg)
Radius
2.00x Earth (12,742 km)
This planet: 2.00× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.00x Earth (19.6 m/s²)
Surface Temperature
634 K (361 °C / 682 °F)
Rotation Period
309.6 hours/day (slower than Earth)
This planet: 310 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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