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Habitability
0/ 100
Uninhabitable
UPM J1040-3551 Bb rendered in TerraForge from its measured mass, orbit and star

UPM J1040-3551 Bb

Also written UPM J1040 3551 Bb

Brown DwarfUninhabitable82 light years awayFound 2025
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

UPM J1040-3551 Bb, from the Extrasolar Planets Encyclopaedia (found 2025). Measured: 5720 Earth masses, 1660 AU, a 3200 K M-type star. Composition inferred from a mass of 5720 Earths, which is giant territory whatever its 3.23x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

UPM J1040-3551

Type
M-type (Red Dwarf)
Spectral type
M4V
Temperature
3,200 K
Radius
0.262 ☉
Mass
0.235 ☉
Known planets
2, including this one
Luminosity
6.48e-3 ☉

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?
UPM J1040-3551 Bb 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: 5720.0x EarthTemperature: 751K

Reading UPM J1040-3551 Bb’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while UPM J1040-3551 Bb 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.UPM J1040-3551 Bb sits about 83 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.
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Habitability ScoreUninhabitable
0
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for 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
5720.00x Earth (3.42e+28 kg)
Radius
17.88x Earth (113,939 km)
This planet: 17.88× Earth radiusEarth: 1× (baseline)
Surface Gravity
17.88x Earth (175.4 m/s²)
Surface Temperature
751 K (477 °C / 891 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
1660.00 AU (248 billion km)
Orbital Period
123,481 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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