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Entering orbit…
Habitability
0/ 100
Uninhabitable
XO-3 b rendered in TerraForge from its measured mass, orbit and star

XO-3 b

Also written XO-3b, XO 3b, XO 3 b

Brown Dwarf694 light years awayFound 2007
Mass
4220.00 × Earth
Radius
14.80 × Earth
Gravity
19.27 g
Surface (est.)
1,888 K
Year
3.2 days
From Earth
695 ly
Mass
4220.00 × Earth
Radius
14.80 × Earth
Gravity
19.27 g
Surface (est.)
1,888 K
Year
3.2 days
From Earth
695 ly

XO-3 system

Type
F-type (White)
Spectral type
F5V
Temperature
6,970 K
Radius
1.52 ☉
Mass
1.45 ☉
Planets
1
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.

XO-3 b0.048 AUYou are here4,220 M⊕
Habitable zone

Star and planets drawn to scale: the star is 11 times as wide as XO-3 b, so only its edge is in view. Orbits spaced as in the star system view.

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.

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
XO-3 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: 4220.0x EarthTemperature: 1888K

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.
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 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
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

Time Dilation

Clocks run 12.6 seconds per year slower than deep space — about 17 minutes over a lifetime

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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