Exploring K2-18b: Could This Exoplanet Contain Life?

Monday - September 18 2023, 16:51 UTC - 1 year ago

K2-18b is an exoplanet about 124 light-years from Earth, recently observed by the James Webb Space Telescope. Scientists in the UK and US have detected chemical traces in the planet's atmosphere that suggest potential signs of life. Earth-based telescopes are now attempting to monitor the planets' atmospheres as it passes in front of its star in order to detect more signs of potential life.

Are we alone? This question is nearly as old as humanity itself. Today, the 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.Meet Exoplanet K2-18bK2-18b 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).Earth is what is called a rocky planet (for obvious reasons) but sub-Neptunes are gas planets, with much larger atmospheres containing lots of hydrogen and helium. Their atmosphere can also contain other elements .

Which brings us to the excitement around K2-18b.How to Fingerprint an AtmosphereThe planet was first discovered by the Kepler Space Telescope, which was monitoring distant stars and hoping for planets to pass in front of them. When a planet does pass between us and a star, the star becomes momentarily dimmer—which is what tells us a planet is there.By measuring how big the dip in brightness is, how long it takes for the planet to pass in front of the star, and how often this happens, we can work out the size and orbit of the planet .

This technique is great at finding planets, but it doesn’t tell us about their atmospheres—which is a key piece of information to understand if they hold life or are habitable.NASA’s James Webb Space Telescope—the big space telescope launched at the end of 2021—has now observed and measured the atmosphere of this exoplanet.The telescope did this by measuring the color of light so finely, it can detect traces of specific atoms and molecules .

This process, called spectroscopy, is like measuring the fingerprints of elements.Each element and molecule has its own color signature. If you can look at the color signature, you can do a bit of detective work, and figure out what elements or compounds are in the planet.While the planet does not have its own light, astronomers waited for when K2-18b passed in front of its star so that they could record the light that had passed through its atmosphere .