Analysis finds evidence for many exoplanets made of water and rock around small stars

According to a recent study, many planets may have half rock and half water, which is more water than was previously believed. All that water may have been confined inside the rock rather than rising to the surface as rivers or oceans.

The discovery of so many water worlds orbiting the most prevalent form of star in the galaxy surprised Rafael Luque, the paper’s first author and a postdoctoral researcher at the University of Chicago. “It was a surprise to see evidence for so many water worlds,” he said. It has significant ramifications for the search for terraforming planets.

Due to advancements in telescopic technology, researchers are discovering evidence of an increasing number of planets in distant solar systems. Similar to how examining a town’s population as a whole might show tendencies that are difficult to observe at an individual level, a bigger sample size aids scientists in discovering demographic patterns.

To examine a collection of planets that are seen around an M-dwarf star, Luque and co-author Enric Palle of the Institute of Astrophysics of the Canary Islands and the University of La Laguna chose to look at the planets’ populations. Numerous planets have been discovered so far around these stars, which are among the most frequent stars in our galaxy.

However, we are unable to see the planets themselves because the stars are so much brighter than their planets. However, there is subtle evidence of the planets’ influence on their stars that may be seen by scientists, such as the shadow cast as a planet passes in front of its star and the slight tug on the star’s motion as it orbits. That means there are still a lot of unanswered concerns regarding the appearance of these planets.

According to Palle, “the two different methods of discovering planets each provide you with different information.” Scientists can measure a planet’s diameter by observing the shadow that is cast as it passes in front of its star. Its mass can be determined by measuring the minuscule gravitational attraction that a planet has on a star.

By combining the two studies, researchers can better understand the composition of the planet. It could be a large, airy planet like Jupiter, which is presumably made up of gas, or it could be a small, dense, rocky planet like Earth.

Individual planets have been subjected to these analyses, but the aggregate study of such planets in the Milky Way Galaxy has rarely been done. When studying data on a total of 43 planets, scientists noticed a startling pattern emerging.

Most of the planets’ densities indicated that they were too light to be entirely composed of rock because of their size. Instead, these planets are most likely made up of a mixture of water or another lighter molecule and rock. Try picking up a soccer ball and a bowling ball; they are both about the same size, but one is made of a much lighter material.

It could be tempting to picture these worlds as being fully submerged beneath vast oceans, like something from Kevin Costner’s Waterworld. These planets are so close to their suns, though, that any surface water would be in a supercritical gaseous phase, increasing the radius of the planets. However, Luque said, “We don’t see that in the samples.”

instead, the water can be present in pockets below the surface or incorporated with the rock. In those circumstances, the moon Europa of Jupiter, which is thought to have liquid water beneath, would be comparable.

“I was astonished when I saw this research,” said U Chicago exoplanet scientist Jacob Bean, whose group Luque has joined to do additional analyses. “I, and many people in the field, assumed these were all dry, rocky worlds,” he said.

The discovery supports an exoplanet formation theory that has lost favor in recent years, which postulates that many planets form farther outside of their solar systems and move closer in over time.


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