Where are the water worlds? New tool to find out (earthsky.org)

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Posted by Paul Scott Anderson and Deborah Byrd
October 6, 2021

Water worlds? Or thick atmospheres?

Water is common in our solar system. We find it in both liquid and ice form, on Earth and other planets. And water is key to life as we know it. How about in distant solar systems? How many exoplanets – worlds orbiting distant stars – have water? Is water on exoplanets common … or rare? We don’t know yet, in part because it’s been hard to tell the difference between an ocean planet and one with a thick hydrogen atmosphere. Now, in a study being called a potential breakthrough, a team of researchers has figured out a way to test for water on sub-Neptune exoplanets, including some of the larger super-Earths.

The study has been accepted for publication in the peer-reviewed Astrophysical Journal Letters. It can currently be read in preprint form on arXiv. The new research comes from Caltech, MIT, and other institutions. Planetary scientist Renyu Hu at NASA’s Jet Propulsion Laboratory is the lead author. Hu told EarthSky in an email:

[Our] paper mostly addresses planets in the 1.7-3.5 Earth-radii range. From the exoplanet survey of Kepler and many follow-up observations, we now know that the 1.7-3.5 Earth radii planets constitute a different planet population from the {less than}1.7-Earth-radii planets.

The news about Hu and team’s new computer model – designed to reveal water worlds on sub-Neptune exoplanets – was also featured in an article in Inverse on September 1, 2021.

The terminology can get confusing here. There’s overlap between the terms super-Earth, sub-Neptune and mini-Neptune. Super-Earths have a lower upper size limit than mini-Neptunes, but they’re still between Earth and Neptune in size and mass. When you hear super-Earth, think big, rocky world. Kind of like Earth on steroids. A big rocky super-Earth could have oceans on its surface.
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more: https://earthsky.org/space/where-are-the-water-worlds-new-tool-might-reveal-them/?utm_source=EarthSky+News

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