2 alien water worlds discovered with oceans 500 times deeper than Earth’s

Astronomers said in December 2022 that they’ve identified the first true water worlds, unlike any in our solar system. These exoplanets are both slightly larger than Earth. Yet their density lies between that of a rocky world like ours, and our solar system’s gas-giant outer planets. These astronomers believe these worlds must have global oceans at least 500 times deeper than the average depth of Earth’s oceans, which, by contrast, they called simply a wet veneer on a rocky ball. This artist’s illustration shows Kepler-138 d in the foreground, Kepler-138 c and Kepler 138 b, seen in silhouette transiting its star. Kepler-138 c and Kepler-138 d are water worlds a little larger than Earth. But their global oceans are much deeper than Earth’s and warmer, with a hot, steamy water vapor atmosphere above them. Image via NASA/ ESA/ Leah Hustak (STScI)/ Hubblesite. The two worlds orbit a red dwarf star called Kepler-138, which is 218 light-years away in the direction of our constellation Lyra the Harp. Scientists have theorized that global water worlds like these exist. They’ve had some tantalizing hints before now. But these are the first specific worlds for which there is now good evidence. The astronomers made the discovery using data from the Hubble and Spitzer space telescopes. Caroline Piaulet of the Trottier Institute for Research on Exoplanets (iREx) at the University of Montreal, Canada, led the team effort. The researchers published their peer-reviewed findings in Nature Astronomy on December 15, 2022. A free preprint version of the paper is also available on arXiv. We think of Earth, of course, as a water world, with its surface mostly covered by oceans. But these two new exoplanets – Kepler-138 c and Kepler-138 d – appear to have oceans at least 1,000 miles (1,600 km) deep. That’s about 500 times deeper than the average depth of Earth’s oceans. The ocean moons in our own solar system, such as Europa, Enceladus and others, would be the closest analogy. But both of those are much smaller moons, not planets, with a crust of ice over their oceans. These new planets are kind of like much larger and warmer versions of the ocean moons. As Piaulet said: Imagine larger versions of Europa or Enceladus, the water-rich moons orbiting Jupiter and Saturn, but brought much closer to their star. Instead of an icy surface, they would harbor large water-vapor envelopes. So, how did the astronomers discover these water worlds? The Hubble and now-retired Spitzer space telescopes provided the data. When the researchers studied the data, they found something unusual. Both planets are just a little larger than Earth. But they aren’t nearly as dense as Earth or other known rocky planets. They are, however, still denser than the gas or ice giants in the outer solar system. How could that be?