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Entering orbit…
Habitability
0/ 100
Uninhabitable

Reading XO-3 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while XO-3 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.XO-3 b sits about 695 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.

XO-3 b

Brown DwarfUninhabitable694 light years awayFound 2007

XO-3 b, from the NASA Exoplanet Archive (found 2007). Measured: 4220 Earth masses, 0.0481 AU, a 6970 K F-type star. Composition inferred from a mass of 4220 Earths, which is giant territory whatever its 1.30x density suggests, with a day locked to its 3.2-day year, as anything orbiting this close would be.

Host star

XO-3

Type
F-type (White)
Spectral type
F5V
Temperature
6,970 K
Radius
1.52 ☉
Mass
1.45 ☉
Known planets
1 (this one)
Luminosity
4.92 ☉

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: 4220.0x EarthTemperature: 1888K
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 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
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
4220.00x Earth (2.52e+28 kg)
Radius
16.16x Earth (102,954 km)
This planet: 16.16× Earth radiusEarth: 1× (baseline)
Surface Gravity
16.16x Earth (158.5 m/s²)
Surface Temperature
1,888 K (1,615 °C / 2,938 °F)
Rotation Period
76.6 hours/day (slower than Earth)
This planet: 77 h/dayEarth: 24 h/day

Orbital Environment

Star Type
F-type (White)
Distance from Star
0.05 AU (7.2 million km)
Orbital Period
3 days
Time Dilation
Clocks run 12.6 seconds per year slower than deep space — about 17 minutes over a lifetime

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
A binary star system's orrery: two suns close together, a red dashed dead-zone boundary, and a debris trail left by a destroyed world

New: Binary Star Systems 🌀

A system can now orbit two suns. Add a companion star when you build one — close, medium, or wide — and the physics decides what survives: a shared center of mass carves out a dead zone where gravity from both stars tears a world apart, leaving it as debris, and every surviving planet's orbit goes elliptical, moving fastest at closest approach and slowest out at aphelion. Push the separation to wide and the dead zone opens tens of AU across, wide enough to gut a system that would have been stable around one star alone. Stand on a world that made it through and you'll watch two suns cross the sky together.

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