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Entering orbit…
Habitability
12/ 100
Uninhabitable
GJ 4276 b rendered in TerraForge from its measured mass, orbit and star

GJ 4276 b

Also written GJ 4276b

Gas Giant69 light years awayFound 2019
Mass
16.60 × Earth
Radius
4.22 × Earth
Gravity
0.93 g
Surface (est.)
378 K
Year
13.4 days
From Earth
69.5 ly
Mass
16.60 × Earth
Radius
4.22 × Earth
Gravity
0.93 g
Surface (est.)
378 K
Year
13.4 days
From Earth
69.5 ly

GJ 4276 system

Type
M-type (Red Dwarf)
Spectral type
M4.0
Temperature
3,387 K
Radius
0.407 ☉
Mass
0.406 ☉
Planets
2
Luminosity
0.0197 ☉

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 4276 c0.052 AU4.3 M⊕
GJ 4276 b0.082 AUYou are here17 M⊕
Habitable zone

Star and planets drawn to scale: the star is 11 times as wide as GJ 4276 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 4276 b, from the NASA Exoplanet Archive (found 2019). Measured: 16.6 Earth masses, 0.082 AU, a 3387 K M-type star. Composition inferred from a estimated bulk density of 0.22x 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 18% hydrogen/helium envelope by mass, with a day locked to its 13.4-day year, as anything orbiting this close would be.

Surface. No solid surface - thick gaseous envelope with possible rocky core deep within

Gas Giant
Magnetic FieldExtreme Activity
GJ 4276 b has 60.2% hydrogen and helium, combined with a mass of 16.6x Earth, which exceeds the gas giant threshold.
Gas giants form when massive cores capture enormous atmospheres of light gases. They typically form beyond the 'frost line' where volatiles can condense.
Classification Criteria:
✓ Hydrogen + Helium: 60.2% (>60% required)✓ Mass: 16.6x Earth (>10x required)

Reading GJ 4276 b’s atmosphere

Dominant elements: H, O, He, Si, Fe, NThis is what a telescope would measure while GJ 4276 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 4276 b sits about 69 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.
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Habitability ScoreUninhabitable
12
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere18

Hydrogen and helium dominated with trace methane and ammonia

Hydrogen-rich atmosphere typical of gas giants (partially stripped by slow rotation)
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - days and nights each last several Earth days, bringing extreme temperature swings

Physical Properties

Mass
16.60x Earth (9.91e+25 kg)
Radius
2.55x Earth (16,252 km)
This planet: 2.55× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.55x Earth (25.0 m/s²)
Surface Temperature
378 K (105 °C / 221 °F)
Rotation Period
321.6 hours/day (slower than Earth)
This planet: 322 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.

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