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Entering orbit…
Habitability
0/ 100
Uninhabitable
RX J1608.9-3905 Ab rendered in TerraForge from its measured mass, orbit and star

RX J1608.9-3905 Ab

Also written RX J1608.9 3905 Ab

Brown DwarfUninhabitable505 light years awayFound 2022
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

RX J1608.9-3905 Ab, from the Extrasolar Planets Encyclopaedia (found 2022). Measured: 6770 Earth masses, 7540 AU, a 4715 K K-type star. Composition inferred from a mass of 6770 Earths, which is giant territory whatever its 3.92x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

RX J1608.9-3905 A

Type
K-type (Orange)
Spectral type
K2
Temperature
4,715 K
Radius
1.81 ☉
Mass
1.4 ☉
Known planets
1 (this one)
Luminosity
1.46 ☉

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

Brown Dwarf

Magnetic FieldNone Activity
Why is this a Brown Dwarf?
RX J1608.9-3905 Ab 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: 6770.0x EarthTemperature: 1105K

Reading RX J1608.9-3905 Ab’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while RX J1608.9-3905 Ab 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.RX J1608.9-3905 Ab sits about 506 light-years away. 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
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 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
6770.00x Earth (4.04e+28 kg)
Radius
18.92x Earth (120,523 km)
This planet: 18.92× Earth radiusEarth: 1× (baseline)
Surface Gravity
18.92x Earth (185.6 m/s²)
Surface Temperature
1,105 K (832 °C / 1,530 °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
7540.00 AU (1.13 trillion km)
Orbital Period
782,543 years

Atmosphere

Hydrogen and helium dominated by methane absorption, with water clouds below

Elemental Composition

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

Surface Characteristics

No surface: a cooling failed star, its methane atmosphere absorbing so much red light it would look magenta to the eye
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The surface of TOI-700 d as TerraForge draws it: red-leaved trees over green ground under a lavender sky

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