Researchers developed computer simulations of Jupiter's growth and tracked how its gravity caused rapid collisions between rocky and water-rich planetesimals in the early solar system.
Four and a half billion years ago, Jupiter rapidly grew to its enormous size. Its strong gravitational pull disrupted the orbits of small, rocky, icy bodies—similar to today’s asteroids and comets—called planetesimals. This caused them to collide with each other at such high speeds that the rock and dust inside them melted upon impact, forming floating droplets of molten rock—chondrules—that we find preserved in meteorites today.
Now, researchers from Nagoya University in Japan and the Italian National Institute for Astrophysics (INAF) have determined for the first time how these droplets formed and have used their findings to precisely date Jupiter's formation. Their study, published in Scientific Reports , shows how the characteristics of chondrules—particularly their size and the rate at which they cooled in space—are determined by the water contained in the colliding planetesimals. This explains observations in meteorite samples and proves that chondrule formation was a result of planet formation processes.
Time capsules from 4.6 billion years ago
Chondrules—small spheres about 0.1–2 mm in diameter—were incorporated into asteroids as the solar system formed. Billions of years later, pieces of those asteroids broke off and fell to Earth as meteorites. (The question) How chondrules acquired their round shape has occupied scientists for decades.
"When the planetesimals collided with each other, the water instantly evaporated into expanding steam. This acted like tiny 'explosions' and shattered the molten silicate rock into the tiny droplets we see in meteorites today," explains Professor Sin-iti Sirono, co-lead author from Nagoya University's School of Earth and Environmental Studies.
"Previous theories of formation were unable to explain the characteristics of chondrules without requiring very specific conditions, while this model is satisfied with conditions that arose naturally in the early solar system at the time of Jupiter's birth."
The researchers developed computer simulations of Jupiter's growth and tracked how its gravity caused rapid collisions between rocky and water-rich planetesimals in the early solar system.
"We compared the properties and abundance of simulated chondrules with meteorite data, and found that the model spontaneously creates realistic chondrules. The model also shows that the production of chondrules coincides with the intense accretion of nebular gas by Jupiter until it reached its enormous mass. Since meteorite data indicate that the peak of chondrule formation occurred 1.8 million years after the beginning (formation) of the Solar System, this is also the time when Jupiter was born (formed)," says Dr. Diego Turrini, co-lead author and senior researcher at INAF.
A new way to date the formation of planets
The study provides a clearer picture of how our solar system formed. However, the production (formation) of chondrules that began with the formation of Jupiter is too short to explain why we find many chondrules of different ages in meteorites. The most likely explanation is that other giant planets, such as Saturn, also formed chondrules when they were born.
By studying chondrules of different ages, scientists can trace the order of birth (formation) of planets and understand how our solar system evolved over time. The study also suggests that these violent formation processes may occur around other stars, providing insights into the evolution of other planetary systems.
The study, "Chondrule formation by collisions of planetesimals containing volatiles triggered by Jupiter's formation," was published in the journal Scientific Reports on August 25, 2025. DOI: 10.1038 / s41598-025-12643-x.
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Water in meteorites – this is literally "the water that is above the sky."