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Entering orbit…
Habitability
11/ 100
Uninhabitable
GJ 3929 b rendered in TerraForge from its measured mass, orbit and star

GJ 3929 b

Also written GJ 3929b

Rocky Terrestrial52 light years awayFound 2022
Mass
1.75 × Earth
Radius
1.09 × Earth
Gravity
1.47 g
Surface (est.)
574 K
Year
2.6 days
From Earth
51.5 ly
Mass
1.75 × Earth
Radius
1.09 × Earth
Gravity
1.47 g
Surface (est.)
574 K
Year
2.6 days
From Earth
51.5 ly

GJ 3929 system

Type
M-type (Red Dwarf)
Spectral type
M3.5 V
Temperature
3,384 K
Radius
0.32 ☉
Mass
0.313 ☉
Planets
2
Luminosity
0.0109 ☉

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.

GJ 3929 b0.025 AUYou are here1.8 M⊕
GJ 3929 c0.081 AU5.7 M⊕
Habitable zone

Star and planets drawn to scale: the star is 32 times as wide as GJ 3929 b, so only its edge is in view. Orbits spaced as in the star system view.

GJ 3929 b, from the NASA Exoplanet Archive (found 2022). Measured: 1.75 Earth masses, 0.0252 AU, a 3384 K M-type star. Composition inferred from a measured bulk density of 1.35x Earth's, which is rock and iron, with a day locked to its 2.6-day year, as anything orbiting this close would be.

Surface. Rocky surface with impact craters, possible volcanic features

Rocky Terrestrial
Life unlikely — too hot for liquid waterMagnetic FieldModerate Activity
GJ 3929 b is dominated by silicate (25.0%) and iron (12.5%) content, forming a rocky terrestrial body.
Rocky terrestrial planets are primarily composed of silicate rocks and metals. They're the most common type of small planet in the universe.
Classification Criteria:
✓ Silicon: 25.0% + Iron: 12.5% + Magnesium: 3.8%✓ Mass: 1.8x Earth (terrestrial range)

Reading GJ 3929 b’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while GJ 3929 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.GJ 3929 b sits about 52 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
11
Contributing Factors
temperature6
Extremely hot - hostile to known life forms
atmosphere70

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable
water12
Limited water content - boiling away, little would be retained
magnetic Field100
Magnetic field provides radiation protection
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
1.75x Earth (1.05e+25 kg)
Radius
1.21x Earth (7,678 km)
This planet: 1.21× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.21x Earth (11.8 m/s²)
Surface Temperature
574 K (301 °C / 574 °F)
Rotation Period
62.9 hours/day (slower than Earth)
This planet: 63 h/dayEarth: 24 h/day

Time Dilation

Clocks run 5.6 seconds per year slower than deep space — about 7 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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