Astronomers have discovered that planet formation in our young solar system began much earlier than previously thought, with the building blocks of planets growing at the same time as their parent stars. The building blocks for planets like Jupiter and Saturn are probably starting to form as a young star grows, according to a study of some of the oldest stars in the universe. Previously, planets were thought to form only when a star reached its final size, but new results have been published in the journalism. Nature Astronomyshow that stars and planets “grow” together.

Cambridge University-led research is changing our understanding of how planetary systems form, including our own solar system, and potentially solving a great mystery in astronomy.

“We have a pretty good idea of ​​how planets formed, but we have an important question about when they formed: Does planet formation begin early when the parent star is still growing, or does it occur millions of years later?” said first author of the study, Dr. Amy Bonsor.

To try to answer this question, Bonsor and colleagues investigated the atmospheres of white dwarf stars — ancient, faint remnants of stars like our Sun — to study the building blocks of planet formation. Researchers from the University of Oxford, the Ludwig-Maximilians-University of Munich, the University of Groningen and the Max Planck Solar System Research Institute in Göttingen also participated in the study.

“Some white dwarfs are wonderful laboratories because their thin atmospheres are almost like graveyards in the sky,” Bonsor said.

Usually telescopes cannot reach the interiors of planets. But a special class of white dwarfs, known as “dirty” systems, normally contain heavy elements such as magnesium, iron and calcium in their clean atmospheres. These elements likely come from small bodies, such as asteroids, left over from the formation of planets that crashed into white dwarfs and burned up in their atmospheres. As a result, spectroscopic observations of dirty white dwarfs can probe the interior of these fragmented asteroids and give astronomers direct insight into the conditions under which they formed.

Planet formation is thought to have begun in a protoplanetary disk composed mostly of hydrogen, helium and small particles of ice and dust orbiting a young star. According to the current leading theory of how planets form, dust particles stick together, eventually forming larger and larger solids. Some of these massive objects will continue to coalesce into planets, while others will remain asteroids, such as those that hit white dwarfs in the current study.

The researchers analyzed spectroscopic observations of the atmospheres of 200 dirty white dwarfs from nearby galaxies. According to their analysis, the mix of elements seen in these white dwarfs’ atmospheres can only be explained if once most of the parent asteroids melted, causing heavy iron to sink into the core and lighter elements to float on the surface. This process, known as differentiation, is why Earth has an iron-rich core.

“The reason for the meltdown can be explained by very short-lived radioactive elements that only exist in the early stages of the planetary system but decay in just a million years,” Bonsor said. Said. “In other words, if these asteroids were melted down by something that existed very briefly at the dawn of the planetary system, then the planet formation process must have started very quickly.”

The study shows that the early formation chart is likely correct, meaning that Jupiter and Saturn have had ample time to grow to their current sizes.

“Our work adds to the growing consensus that planet formation begins early, when the first bodies formed at the same time as the star,” said Bonsor. “Analysis of contaminated white dwarfs tells us that this radioactive melting process is a potentially ubiquitous mechanism that affects the formation of all extrasolar planets.

“This is just the beginning – every time we find a new white dwarf, we can gather more evidence and learn more about how planets form. We can trace elements like nickel and chromium and tell how big the asteroid must have been when it formed the iron core. It’s amazing that we can study it in systems.”