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Critical Topics and Their Significance for the UPSC CSE Examination on April 21, 2025

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Does the planet K2-18b show signs of life?

For Preliminary Examination: Current events of national and international Significance

For Mains Examination: GS III - Science & Technology

Context:

On April 16, an international research team uploaded a paper in which it reported that the distant exoplanet K2-18b may be habitable. The claim was met with cautious excitement by astronomers. While finding places in the universe that could harbour life is a vital quest in the field, experts — including the team that made the finding — are cautious because many similar claims in the past have had to be retracted after closer inspection.

Read about:

K2-18b Planet

What is an exoplanet?

Key takeaways:

• K2-18b is an intriguing exoplanet—meaning a planet that exists outside our solar system—located about 124 light-years away from Earth in the constellation Leo. It orbits a red dwarf star known as K2-18 and was first discovered in 2015 by NASA’s Kepler Space Telescope.
• What makes K2-18b particularly fascinating to scientists is that it lies within its star's habitable zone, the region where conditions might be suitable for liquid water to exist on a planet’s surface—a key ingredient for life as we know it.
• K2-18b is significantly larger than Earth, with a radius more than five times wider and a mass nearly nine times greater. These proportions place it between Earth and Neptune in terms of size and composition, leading researchers to suggest it could be a “Hycean world”—a type of planet that might be covered in a deep global ocean beneath a thick, hydrogen-rich atmosphere. This classification remains unconfirmed, but it has opened up new possibilities in the search for potentially habitable planets.
• Over the years, K2-18b has been the subject of detailed atmospheric studies. In 2019, the Hubble Space Telescope detected signs of water vapour in its atmosphere, a major milestone in exoplanet research.
• Later, in 2023, the James Webb Space Telescope (JWST) identified the presence of other important molecules such as methane and carbon dioxide. These compounds are considered potential biosignatures—indicators that could suggest biological processes.
• There were even tentative findings of dimethyl sulphide (DMS), a molecule on Earth primarily associated with life, although this detection remains under debate.
• Despite the excitement, scientists caution that many of these findings are still open to interpretation. The presence of certain molecules doesn’t guarantee life, as they could also be produced through non-biological chemical reactions.
• Moreover, some recent studies have challenged the idea that K2-18b is truly habitable, proposing instead that it might be a gas-rich mini-Neptune with harsh, life-prohibiting conditions.
• Nevertheless, K2-18b remains a compelling subject in the ongoing exploration of exoplanets, offering valuable insights into how planets beyond our solar system might look, behave, and—possibly—host life

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