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This illustration shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light years from Earth. A new investigation with NASA’s James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. In this illustration, the exoplanet K2-18 c is shown between K2-18 b and its star.

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This illustration shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light years from Earth. A new investigation with NASA’s James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. In this illustration, the exoplanet K2-18 c is shown between K2-18 b and its star.
https://cdn.fosstodon.org/media_attachments/files/114/353/304/943/539/247/original/b2ebc5c508994458.jpg

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AkaSci 🛰️ (akasci@fosstodon.org)'s status on Thursday, 17-Apr-2025 21:35:17 JST AkaSci 🛰️
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K2-18b is an exoplanet orbiting the red dwarf K2-18, 124 light-years from Earth. The planet is a sub-Neptune about 2.6x the size of Earth and lies within the star's habitable zone.
Radius: 2.6x Earth
Mass: 8.63x Earth
Orbital radius: 0.16 AU
Atmosphere: Hydrogen with small amounts of CO2, Methane and possibly DMS. Low on water vapor and ammonia.
Temp: around −8°C
A liquid water ocean has been hypothesized (a Hycean), but evidence is weak.
https://webbtelescope.org/contents/media/images/2023/139/01H9R88HG8YXRMARWZ5B1YDT27
https://en.wikipedia.org/wiki/K2-18b#
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