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Entering orbit…
Habitability
0/ 100
Uninhabitable

HD 81817 b

Brown DwarfUninhabitable877 light years awayFound 2020

HD 81817 b, from the NASA Exoplanet Archive (found 2020). Measured: 7670 Earth masses, 3.23 AU, a 4140 K K-type star. Composition inferred from a mass of 7670 Earths, which is giant territory whatever its 4.44x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets. Note: TerraForge comes out at 1648 K against the archive's 1016 K, because it models stars by spectral class, and HD 81817 is not an average K-type.

Host star

HD 81817

Type
K-type (Orange)
Spectral type
K3 III
Temperature
4,140 K
Radius
83.8 ☉
Mass
4.3 ☉
Known planets
2, including this one
Luminosity
1.82e+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.

Brown Dwarf

Magnetic FieldNone Activity
Why is this a Brown Dwarf?Your planet 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: 7670.0x EarthTemperature: 1648K
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.
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
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere30
Hydrogen-rich atmosphere typical of gas giants
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
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
7670.00x Earth (4.58e+28 kg)
Radius
19.72x Earth (125,643 km)
This planet: 19.72× Earth radiusEarth: 1× (baseline)
Surface Gravity
19.72x Earth (193.5 m/s²)
Surface Temperature
1,648 K (1,375 °C / 2,507 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
3.23 AU (483 million km)
Orbital Period
6.94 years

Atmosphere

Hydrogen and helium with iron and silicate cloud decks - hot enough to rain molten metal

Elemental Composition

H - Hydrogen
53.8%
He - Helium
32.3%
O - Oxygen
5.4%

Surface Characteristics

No surface: a deuterium-burning sphere the size of Jupiter and dozens of times its mass, glowing dull red from its own heat
The TerraForge exoplanet catalog: 5,572 real exoplanets run through the simulation, with a search field and rendered worlds grouped by type

New: The Exoplanet Catalog 🔭

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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