For centuries, no one knew whether we were alone in the universe – whether other planets like ours existed. But thanks to new telescopes and techniques over the last decades, we now know that thousands and thousands of planets orbit distant stars, and they come in all shapes and sizes – big and small, rocky and gaseous, cloudy and icy. or wet

A study by scientists from the University of Chicago, Michigan and the University of Maryland adds another to the list: planets with helium atmospheres. Also, the discovery could offer a new step in our understanding of the evolution of the planet. Their simulations showed that helium is likely to accumulate in the atmospheres of certain types of exoplanets over time. If confirmed, it would explain a long-standing mystery about the size of these exoplanets.

“There are many strange and wonderful types of exoplanets, and this discovery not only adds a new species, but may have implications for understanding the evolution and formation of planets in general,” said astrophysicist Leslie Rogers of the University of Chicago. new newspaper published in Nature Astronomy .

the secret of radius valley

It took us so long to find distant planets because even the largest ones are dwarfed by the stars they orbit. So scientists came up with an ingenious way to detect them: by looking at the diminution of the star’s light as a planet passes in front of it. This tells you how big the planet is.

We now know that planets are incredibly common. In fact, from what we can now say, at least half of all stars like our Sun have at least one Earth-Neptune-sized planet orbiting very close to the star. These planets are assumed to have atmospheres rich in hydrogen and helium, which were collected when the planets first formed from the gas and dust around the star.

But when scientists looked at the number of such planets, they noticed something interesting – the planets were divided into two groups. One group was about the size of an Earth and a half, and the other group was twice the size of Earth or larger, but there were hardly any in between.

This gap between the two planetary populations is known as the “valley radius” and is a hotly debated topic in the field. Scientists believe the answer will help us understand how this and other planets formed and evolved over time. Some have suggested that the explanation for this gap may have to do with the atmospheres of the planets. Being a planet close to its star is difficult; you are constantly being bombarded with x-rays and ultraviolet rays that can destroy your atmosphere.

“For example, it is possible for a smaller group of planets to lose their atmospheres completely and simply exist as rocky cores,” said Isaac Malsky, first author of the study. The student at the University of Michigan who first began exploring this question with Rogers for his thesis at the University of Chicago.

The team, including Rogers and Malsky, decided to take a closer look at this phenomenon, known as atmospheric escape. They built models based on the data we have of planets and the laws of physics to better understand how heat and radiation would affect planetary atmospheres. They then created 70,000 simulated planets by changing the size of the planets, the type of star they orbit, and the temperature of the atmosphere, and simulated what would happen to them over time.

The team found that after a few billion years, hydrogen in planetary atmospheres will escape faster than helium. “Hydrogen has a lower atomic mass, so it’s easier to isolate,” Malsky explained. Over time this leads to helium buildup – simulations have shown that helium can make up 40% or more of the atmosphere’s mass.

Confirmation of the telescope

The team proposed a way to confirm their results with observations. The recently launched James Webb Space Telescope and other powerful telescopes can read atmospheric elements and their abundances. Telescopes can test for unusually large amounts of helium in the atmospheres of some of these planets. If the theory is correct, these planets with helium-rich atmospheres should be common, especially in the lower part of the larger radius group because helium is accumulating as the planet’s atmosphere gradually empties and begins to shrink over time.

Malsky explained that two different sized groups of planets were created because even small amounts of helium and hydrogen create a very loose atmosphere that can greatly increase the radius of the planet. If they have any atmosphere left, they will be in a group with a larger radius; if there are none, they will be in a group with a smaller radius.

None of these planets are considered suitable candidates for life; They are hot, bombarded with radiation, and their atmospheres are probably under very high pressure. But scientists explained that improving our understanding of the processes that drive planet formation could help us better predict the existence of other planets and what they might look like, and guide the search for more hospitable planets.

“A better understanding of this population can tell us a lot about the origin and evolution of Neptune-sized planets, which is apparently a common result of the planet formation process,” Rogers said. Said.