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Entering orbit…
Habitability
35/ 100
Extremely Harsh
LP 791-18 d rendered in TerraForge from its measured mass, orbit and star

LP 791-18 d

Also written LP 791-18d, LP 791 18d, LP 791 18 d

Rocky Terrestrial86 light years awayFound 2023
Mass
0.91 × Earth
Radius
1.03 × Earth
Gravity
0.86 g
Surface (est.)
447 K
Year
2.8 days
From Earth
86.4 ly
Mass
0.91 × Earth
Radius
1.03 × Earth
Gravity
0.86 g
Surface (est.)
447 K
Year
2.8 days
From Earth
86.4 ly

LP 791-18 system

Type
M-type (Red Dwarf)
Spectral type
M(6.1 +/- 0.7) V
Temperature
2,960 K
Radius
0.182 ☉
Mass
0.139 ☉
Planets
3
Luminosity
2.30e-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.

LP 791-18 b0.010 AU1.9 M⊕
LP 791-18 d0.020 AUYou are here0.9 M⊕
LP 791-18 c0.030 AU7.2 M⊕
Habitable zone

Star and planets drawn to scale: the star is 19 times as wide as LP 791-18 d, so only its edge is in view. Orbits spaced as in the star system view.

LP 791-18 d, from the NASA Exoplanet Archive (found 2023). Measured: 0.91 Earth masses, 0.0199 AU, a 2960 K M-type star. Composition inferred from a measured bulk density of 0.83x Earth's at this size, suggesting roughly 11% water/ice by mass, with a day locked to its 2.8-day year, as anything orbiting this close would be.

Surface. Rocky surface with impact craters, possible volcanic features

Rocky Terrestrial
Life unlikely — too hot for liquid waterMagnetic FieldModerate Activity
LP 791-18 d is dominated by silicate (22.4%) and iron (11.3%) 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: 22.4% + Iron: 11.3% + Magnesium: 3.3%✓ Mass: 0.9x Earth (terrestrial range)

Reading LP 791-18 d’s atmosphere

Dominant elements: O, Si, H, Fe, N, CThis is what a telescope would measure while LP 791-18 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.LP 791-18 d sits about 86 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 ScoreExtremely Harsh
35
Contributing Factors
temperature12
Extremely hot - hostile to known life forms
atmosphere70

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable
water65
Good water content - likely as steam
magnetic Field100
Magnetic field provides radiation protection
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
0.91x Earth (5.43e+24 kg)
Radius
0.97x Earth (6,174 km)
This planet: 0.97× Earth radiusEarth: 1× (baseline)
Surface Gravity
0.97x Earth (9.5 m/s²)
Surface Temperature
447 K (174 °C / 345 °F)
Rotation Period
66.0 hours/day (slower than Earth)
This planet: 66 h/dayEarth: 24 h/day

Time Dilation

Clocks run 7.0 seconds per year slower than deep space — about 9 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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