The various processes that lead to the formation of rocky planets are relatively well known today. But there are still certain points on which there is no real consensus, especially when it comes to the very beginning of the process. Current models all suggest that the story begins with a kind of seed around which material will then agglomerate. But the exact nature of this seed remains quite mysterious.
Frozen adventurers at the origins of planets
One of the most promising theories is that planet formation begins with small pieces of rock covered in ice that populate the outside of protoplanetary disks – the circular clumps that contain the material that nascent planets feed on.
Under the influence of friction with the surrounding material, they then drift towards the hot region surrounding the young star. Once close enough, rwater vapor is released which plays an important role in the rest of the process. This is a solid hypothesis, but no one has been able to confirm it because no instrument has ever managed to document these dynamics.
However, this has just changed thanks to the James Webb Space Telescope, and this discovery offers a new perspective on the formation of terrestrial planets such as Earth.
Compact discs are more loaded with water
It all started with the observation of four protoplanetary disks – two quite compact, and two very extensive. They orbited stars from the same family as the sun. The difference is that these stars were all 2 to 3 million years old, compared to about 4.6 billion years for our favorite star. So it was about baby stars.
In theory, the drift of icy rocks should be greater in the central regions of the most compact disks than with extended drives.
This hypothesis arises from the fact that larger disks tend to be cut into several distinct zones by areas where pressure is greater. Researchers call them pressure drops. They correspond to the dark areas to the right of the artist’s impression below.
What’s important is that these are difficult obstacles to overcome. She significantly slow the drift of frozen material into the central zone. Therefore, when more water is found in the central part of compact discs that for extended disks it is a very strong argument to claim that it comes directly from the peripheral zone.
This is exactly what MIRI, Webb’s infrared spectrometer, observed. The data confirmed that there was indeed excess water in the central region of the smaller, denser disks, where the ice can float freely without falling into a pressure drop. By extension, this strongly suggests that it is indeed these frozen rocks that serve as the starting point for rocky planets, as the theory suggests.
A clue to the origin of the earth
And for the researchers the conclusion is crystal clear – that is true; this is the most convincing demonstration yet Rocky planets like Earth were just small pebbles covered in ice at the beginning of their history.
“ The Webb eventually revealed the connection between water vapor in the inner disk and frozen rocks in the outer disk ” said Andrea Banzatti, an astrophysicist at Texas State University and lead author of the study.
“ In the past we had this very static view of planet formation, as if there were isolated regions from which planets emerged. », specifies his colleague Colette Salyk. “ Now we have evidence that these areas interact with each other “.
This work also testifies to that the incredible versatility of the James Webb Telescope instruments. Although it specializes in the hunt for the origins of the universe, by studying objects more than 13 billion light years away, it is also able to provide us with information directly related to the history of our good old blue planet.