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Entering orbit…
Habitability
10/ 100
Uninhabitable
2MASS J1258+2630 b rendered in TerraForge from its measured mass, orbit and star

2MASS J1258+2630 b

Also written 2MASS J1258+2630b

Gas Giant191 light years awayFound 2021
Mass
1080.00 × Earth
Radius
13.00 × Earth
Gravity
6.39 g
Surface (est.)
490 K
Year
11.9 days
From Earth
191 ly
Mass
1080.00 × Earth
Radius
13.00 × Earth
Gravity
6.39 g
Surface (est.)
490 K
Year
11.9 days
From Earth
191 ly

2MASS J1258+2630 system

Type
K-type (Orange)
Spectral type
M1.3V
Temperature
3,825 K
Radius
0.602 ☉
Mass
0.59 ☉
Planets
1
Luminosity
0.0699 ☉

Published by the Extrasolar Planets Encyclopaedia. This world’s temperature and habitability score are computed from its star’s published radius and temperature.

2MASS J1258+2630 b0.086 AUYou are here1,080 M⊕
Habitable zone

Star and planets drawn to scale: the star is 5.1 times as wide as 2MASS J1258+2630 b, so only its edge is in view. Orbits spaced as in the star system view.

exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

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

2MASS J1258+2630 b, from the Extrasolar Planets Encyclopaedia (found 2021). Measured: 1080 Earth masses, 0.0855 AU, a 3825 K K-type star. Composition inferred from a mass of 1080 Earths, which is giant territory whatever its 0.49x density suggests, with a day locked to its 11.9-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
2MASS J1258+2630 b has 86.0% hydrogen and helium, combined with a mass of 1080.0x 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: 86.0% (>60% required)✓ Mass: 1080.0x Earth (>10x required)

Reading 2MASS J1258+2630 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while 2MASS J1258+2630 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.2MASS J1258+2630 b sits about 191 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
10
Contributing Factors
temperature10
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
1080.00x Earth (6.45e+27 kg)
Radius
10.26x Earth (65,366 km)
This planet: 10.26× Earth radiusEarth: 1× (baseline)
Surface Gravity
10.26x Earth (100.6 m/s²)
Surface Temperature
490 K (217 °C / 422 °F)
Rotation Period
285.6 hours/day (slower than Earth)
This planet: 286 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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