Not Only Didn’t We Find Water On An Earth-Like Exoplanet, But We Can’t With Current Technology

“Over the past few decades, astronomers have uncovered thousands of new exoplanets. Some of them are rocky; some are temperate; some have water. However, the idea that exoplanet K2-18b is rocky, Earth-like, and has liquid water is absurd, despite recent headlines. Light filters through K2-18b’s atmosphere when it passes in front of its star, enabling us to measure what’s absorbed. Based on those absorption lines, the presence of many chemicals can be inferred, including water. K2-18b is, truly, the first known habitable-zone exoplanet to contain water. However, it is not rocky; its mass and radius are too large, necessitating a large gas envelope around it.”

How incredible was that report that came out last week: the first Earth-like, rocky exoplanet with liquid water on its surface has been discovered! If it were true, it would be incredible. Well, what we did find is still pretty remarkable, but it’s very different from what you’ve likely heard.

We did find water on the exoplanet in question, K2-18b, but only in the vapor phase and only in the atmosphere.

The exoplanet is closer to Earth in terms of mass and radius than any other with water on it, but the planet is still too massive and large to be rocky. It must have an envelope of hydrogen and helium, and both have had their presence detected.

If we want to find atmospheric biosignatures around Earth-like worlds, we need better observatories. Let’s build them! Here’s the real story.

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astronomy

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