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Entering orbit…
Habitability
0/ 100
Uninhabitable
TOI-3686 b rendered in TerraForge from its measured mass, orbit and star

TOI-3686 b

Also written TOI-3686b, TOI 3686b, TOI 3686 b

Sub-NeptuneUninhabitable841 light years awayFound 2026
exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

TOI-3686 b, from the Extrasolar Planets Encyclopaedia (found 2026). Measured: 10.5 Earth masses, 0.037 AU, a 5990 K G-type star. Composition inferred from a measured bulk density of 0.46x Earth's, too low for bare rock at this size, suggesting a rocky core under roughly a 6% hydrogen/helium envelope by mass, with a day locked to its 2.5-day year, as anything orbiting this close would be.

Host star

TOI-3686

Type
G-type (Yellow (Sun-like))
Spectral type
G0V
Temperature
5,990 K
Radius
1.18 ☉
Mass
1.05 ☉
Known planets
2, including this one
Luminosity
1.63 ☉

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

Gas Dwarf

Magnetic FieldLow Activity
Why is this a Gas Dwarf?
TOI-3686 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: 10.5x EarthTemperature: 1633K

Reading TOI-3686 b’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while TOI-3686 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.TOI-3686 b sits about 841 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.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
0
Contributing Factors
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere30
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
geology60
Some geological activity provides slow nutrient cycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation65
Slow rotation - significant day/night temperature variations, but life can adapt

Physical Properties

Mass
10.50x Earth (6.27e+25 kg)
Radius
2.19x Earth (13,951 km)
This planet: 2.19× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.19x Earth (21.5 m/s²)
Surface Temperature
1,633 K (1,360 °C / 2,480 °F)
Rotation Period
61.0 hours/day (slower than Earth)
This planet: 61 h/dayEarth: 24 h/day

Orbital Environment

Star Type
G-type (Yellow (Sun-like))
Distance from Star
0.04 AU (5.54 million km)
Orbital Period
3 days
Time Dilation
Clocks run 12.6 seconds per year slower than deep space — about 17 minutes over a lifetime

Atmosphere

Deep hydrogen-helium envelope with photochemical haze

Elemental Composition

O - Oxygen
31.3%
Si - Silicon
25.0%
Fe - Iron
12.5%

Surface Characteristics

No solid surface - a hydrogen-helium envelope wrapped around a rocky core (a sub-Neptune)
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The surface of TOI-700 d as TerraForge draws it: red-leaved trees over green ground under a lavender sky

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