Create your free account

Enter your email and we'll send a 6-digit code — no password needed.
We only keep your email and the username you choose. We never share or sell your email, and we don't send marketing — we use it only to email you a sign-in code. Read our privacy policy.
Entering orbit…
Habitability
16/ 100
Uninhabitable
GJ 229 b rendered in TerraForge from its measured mass, orbit and star

GJ 229 b

Also written GJ 229b

Ice Giant19 light years awayFound 2014
Mass
14.90 × Earth
Radius
3.97 × Earth
Gravity
0.95 g
Surface (est.)
113 K
Year
579 days
From Earth
18.8 ly
Mass
14.90 × Earth
Radius
3.97 × Earth
Gravity
0.95 g
Surface (est.)
113 K
Year
579 days
From Earth
18.8 ly

GJ 229 system

Type
M-type (Red Dwarf)
Spectral type
M1.5V
Temperature
3,564 K
Radius
0.46 ☉
Mass
0.509 ☉
Planets
3
Luminosity
0.0280 ☉

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 229 A c0.38 AU8.6 M⊕
GJ 229 c0.90 AU10 M⊕
GJ 229 b1.09 AUYou are here15 M⊕
Habitable zone

Star and planets drawn to scale: the star is 13 times as wide as GJ 229 b, so only its edge is in view. Orbits spaced as in the star system view.

Estimated: this planet doesn't transit its star, so its size is inferred, not measured

GJ 229 b, from the NASA Exoplanet Archive (found 2014). Measured: 14.9 Earth masses, 1.09 AU, a 3564 K M-type star. Composition inferred from a estimated bulk density of 0.24x Earth's, modeled rather than measured since this isn't a transiting planet, larger than even a pure water/ice world of this mass, suggesting a water-rich interior under roughly a 14% hydrogen/helium envelope by mass, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Surface. Icy mantle surrounding rocky core, with hydrogen-helium atmosphere

Ice Giant
Magnetic FieldModerate Activity
GJ 229 b has moderate mass (14.9x Earth) with significant water, carbon, and nitrogen content, characteristic of ice giants.
Ice giants like Uranus and Neptune have icy interiors with thick atmospheres of hydrogen and helium, but not enough to be classified as gas giants.
Classification Criteria:
✓ Mass: 14.9x Earth (5-20x range)✓ Water/Carbon/Nitrogen rich composition

Reading GJ 229 b’s atmosphere

Dominant elements: H, O, Si, He, Fe, NThis is what a telescope would measure while GJ 229 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 229 b sits about 19 light-years away, found by the radial velocity 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.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.
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
16
Contributing Factors
temperature11
Very cold - water frozen, challenging for life
atmosphere30

Hydrogen and helium with water, methane, and ammonia ices

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 Field100
Magnetic field provides radiation protection
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
14.90x Earth (8.90e+25 kg)
Radius
2.46x Earth (15,677 km)
This planet: 2.46× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.46x Earth (24.1 m/s²)
Surface Temperature
113 K (-160 °C / -255 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

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.

Create your free account

Enter your email and we'll send a 6-digit code — no password needed.
We only keep your email and the username you choose. We never share or sell your email, and we don't send marketing — we use it only to email you a sign-in code. Read our privacy policy.

Send feedback

We're still building out the best experience we can — and we'd love your input. Tell us about features you enjoy, ideas you'd like to see, or pain points where something feels off, and we'll know where to look next.

Type
Idea
Bug
Pain point
Other