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Entering orbit…
Habitability
0/ 100
Uninhabitable
G 204-39 b rendered in TerraForge from its measured mass, orbit and star

G 204-39 b

Also written G 204-39b, G 204 39b, G 204 39 b

Brown Dwarf46 light years awayFound 2010
Mass
9220.00 × Earth
Radius
11.90 × Earth
Gravity
65.11 g
Surface (est.)
2,067 K
Year (est.)
254,723 years
From Earth
45.7 ly
Mass
9220.00 × Earth
Radius
11.90 × Earth
Gravity
65.11 g
Surface (est.)
2,067 K
Year (est.)
254,723 years
From Earth
45.7 ly

G 204-39 system

Type
M-type (Red Dwarf)
Spectral type
M3V
Temperature
3,200 K
Mass
0.36 ☉
Planets
1

Published by the Extrasolar Planets Encyclopaedia. This star’s luminosity has not been published, so this world’s temperature and habitability score fall back to a typical M-type star.

G 204-39 b2690.00 AUYou are here9,220 M⊕
Habitable zone

Planets drawn to scale with each other; the star's size is not measured. 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

Estimated: this planet doesn't transit its star, so its size is inferred, not measured

G 204-39 b, from the Extrasolar Planets Encyclopaedia (found 2010). Measured: 9220 Earth masses, 2690 AU, a 3200 K M-type star. Composition inferred from a mass of 9220 Earths, which is giant territory whatever its 5.47x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Surface. No surface: a deuterium-burning sphere the size of Jupiter and dozens of times its mass, glowing dull red from its own heat

Brown Dwarf
Magnetic FieldNone Activity
G 204-39 b 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: 9220.0x EarthTemperature: 2067K

Reading G 204-39 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while G 204-39 b 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.G 204-39 b sits about 46 light-years away, found by the imaging 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
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere30

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

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 Field20
A strong field, but no surface beneath it — there is nothing here for it to shelter
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
9220.00x Earth (5.51e+28 kg)
Radius
20.97x Earth (133,593 km)
This planet: 20.97× Earth radiusEarth: 1× (baseline)
Surface Gravity
20.97x Earth (205.7 m/s²)
Surface Temperature
2,067 K (1,793 °C / 3,260 °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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