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Entering orbit…
Habitability
0/ 100
Uninhabitable
AS 209 b rendered in TerraForge from its measured mass, orbit and star

AS 209 b

Also written AS 209b

Gas GiantUninhabitable394 light years awayFound 2022
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

AS 209 b, from the Extrasolar Planets Encyclopaedia (found 2022). Measured: 413 Earth masses, 200 AU, a 4265 K K-type star. Composition inferred from a mass of 413 Earths, which is giant territory whatever its 0.16x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

AS 209

Type
K-type (Orange)
Spectral type
K5
Temperature
4,265 K
Radius
2.18 ☉
Mass
1.2 ☉
Known planets
1 (this one)
Luminosity
1.42 ☉

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

Gas Giant

Magnetic FieldExtreme Activity
Why is this a Gas Giant?
AS 209 b has 86.0% hydrogen and helium, combined with a mass of 413.0x 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: 413.0x Earth (>10x required)

Reading AS 209 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while AS 209 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.AS 209 b sits about 395 light-years away, found by the imaging 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
Near absolute zero - all molecular activity ceases, impossible for 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
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
413.00x Earth (2.47e+27 kg)
Radius
7.45x Earth (47,445 km)
This planet: 7.45× Earth radiusEarth: 1× (baseline)
Surface Gravity
7.45x Earth (73.1 m/s²)
Surface Temperature
22 K (-252 °C / -421 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
K-type (Orange)
Distance from Star
200.00 AU (29.9 billion km)
Orbital Period
3,381 years

Atmosphere

Hydrogen and helium dominated with trace methane and ammonia

Elemental Composition

H - Hydrogen
53.8%
He - Helium
32.3%
O - Oxygen
5.4%

Surface Characteristics

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