K2-18b is indeed one of the most intriguing exoplanets known, a sub-Neptune (or super-Earth) discovered in 2015 by the Kepler mission's K2 phase. Orbiting a cool red dwarf star 124 light-years away in the constellation Leo, it has a 33-day orbit in the habitable zone, receiving roughly Earth-like stellar radiation. Stunning NASA/ESA artist's impression of K2-18b as a vast ocean world under a hydrogen-rich atmosphere. Classic depiction of the Hycean archetype: a global ocean with no continents, enveloped in thick clouds. Another evocative view showing stormy seas and a hazy sky on this distant water world. Conceptual rendering emphasizing the planet's size compared to Earth, with deep oceans. Dramatic close-up of turbulent waves and atmosphere, capturing the alien ocean vibe. JWST transmission spectrum data hinting at atmospheric composition (methane, CO2, possible others). Hubble-derived artist's concept from earlier water vapor detection era.At ~2.6 times Earth's radius and ~8.6 times its mass, K2-18b is the prototype for Hycean worlds—hypothetical planets with hydrogen-helium atmospheres over global liquid water oceans. JWST observations confirm methane, carbon dioxide, and water vapor in its atmosphere, with no ammonia detected—features consistent with a water-rich interior.However, the "true water world" picture remains debated as of late 2025: some models suggest it could be a gas-rich mini-Neptune with no solid surface, or even have a magma ocean beneath the atmosphere. Early excitement over possible dimethyl sulfide (DMS)—a potential biosignature produced by life on Earth—has largely faded, with reanalyses showing inconclusive or no detection.While not definitively habitable (and any life signals unconfirmed), K2-18b exemplifies the diversity of exoplanets and pushes our understanding of where conditions for life might exist. Ongoing JWST studies continue to refine its nature—truly a captivating window into alien worlds!
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