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Entering orbit…
Habitability
0/ 100
Uninhabitable
ZTF J0220+21 b rendered in TerraForge from its measured mass, orbit and star

ZTF J0220+21 b

Also written ZTF J0220+21b

Brown DwarfUninhabitable1141 light years awayFound 2021
exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

ZTF J0220+21 b, from the Extrasolar Planets Encyclopaedia (found 2021). Measured: 4450 Earth masses, 0.00204 AU, a 14200 K B-type star. Composition inferred from a mass of 4450 Earths, which is giant territory whatever its 20.10x density suggests, with a day locked to its 0.0-day year, as anything orbiting this close would be.

Host star

ZTF J0220+21

Type
B-type (Blue Giant)
Spectral type
DA
Temperature
14,200 K
Radius
0.01 ☉
Mass
0.83 ☉
Known planets
1 (this one)
Luminosity
3.66e-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?
ZTF J0220+21 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: 4450.0x EarthTemperature: 685K

Reading ZTF J0220+21 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while ZTF J0220+21 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.ZTF J0220+21 b sits about 1142 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.
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Habitability ScoreUninhabitable
0
Contributing Factors
temperature5
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere3
Hydrogen-rich atmosphere typical of gas giants (severely compromised by extreme rotation)
water2
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans (water stripped by extreme rotation)
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
rotation0
Catastrophic rotation - centrifugal forces would destroy surface structures and prevent atmosphere retention

Physical Properties

Mass
4450.00x Earth (2.66e+28 kg)
Radius
16.45x Earth (104,792 km)
This planet: 16.45× Earth radiusEarth: 1× (baseline)
Surface Gravity
16.45x Earth (161.4 m/s²)
Surface Temperature
685 K (412 °C / 774 °F)
Rotation Period
1.0 hours/day (faster than Earth)
This planet: 1 h/dayEarth: 24 h/day

Orbital Environment

Star Type
B-type (Blue Giant)
Distance from Star
0.01 AU (1.5 million km)
Orbital Period
0 days
Time Dilation
Clocks run 7.8 minutes per year slower than deep space — about 10.4 hours over a lifetime

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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Open any planet's surface view on your phone and look around just by moving it: hold it up, turn on the spot, and the view turns with you. In Chrome on Android you also get a VR button, in the row along the bottom:

The surface view's bottom row of buttons on a phone, with an arrow pointing to the VR button beside full screen

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