Signs of life? Why astronomers are excited about carbon dioxide and methane in the atmosphere of an alien world Premium

Scientists have just reported some very interesting chemical traces in the atmosphere of a planet called K2-18b, which is about 124 light-years from Earth

Are we alone? This question is nearly as old as humanity itself. Today, this question in astronomy focuses on finding life beyond our planet. Are we, as a species, and as a planet, alone? Or is there life somewhere else?

Usually the question inspires visions of weird, green versions of humans. However, life is more than just us: animals, fish, plants and even bacteria are all the kinds of things we seek signs of in space.

One thing about life on Earth is that it leaves traces in the chemical makeup of the atmosphere. So traces like that, which are visible from a long way away, are something we look for when we’re hunting aliens.

Scientists in the United Kingdom and the United States have just reported some very interesting chemical traces in the atmosphere of a planet called K2-18b, which is about 124 light-years from Earth. In particular, they may have detected a substance which on Earth is only produced by living things.

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K2-18b is an interesting exoplanet – a planet that orbits another star. Discovered in 2015 by the Kepler Space Telescope’s K2 mission, it is a type of planet called a sub-Neptune. As you probably guessed, these are smaller than Neptune in our own Solar System.

The planet is about eight and a half times heavier than Earth, and orbits a type of star called a red dwarf, which is much cooler than our Sun. However, K2-18b orbits much closer to its star than Neptune does – in what we call the habitable zone. This is the area that is not too hot and not too cold, where liquid water can exist (instead of freezing to ice or boiling into steam).