Hidden within meteorites that fall to Earth are tiny spheres that have puzzled scientists for decades. These mysterious droplets, called chondrules, are time capsules from the birth of our Solar System and now, a team from Japan have used them to pinpoint exactly when Jupiter formed, solving a long standing planetary mystery.
Scientists at the Nagoya University in Japan and the Italian National Institute for Astrophysics have discovered that these ancient molten rock droplets, just 0.1 to 2 millimetres wide, formed during Jupiter's violent birth 4.5 billion years ago. Their study, published in Scientific Reports, reveals that Jupiter reached its massive size exactly 1.8 million years after the Solar System began forming.
Jupiter in true colour by Hubble's "Outer Planet Atmospheres Legacy" (Credit : NASA/STSCI)
The story begins in the chaotic early Solar System, when countless rocky and icy bodies called planetesimals orbited the young Sun. As Jupiter rapidly grew to its enormous size, its powerful gravitational pull disrupted these smaller bodies, causing them to collide at incredible speeds. But these weren't ordinary crashes, they were so violent that the rocks melted completely on impact.
"When planetesimals collided with each other, water instantly vaporiSed into expanding steam. This acted like tiny explosions and broke apart the molten silicate rock into the tiny droplets we see in meteorites today” - Professor Sin-iti Sirono from Nagoya University.
The key insight came from understanding the role of water. When water rich planetesimals smashed together, the water didn't just disappear, it explosively turned into steam, acting like microscopic bombs that shattered the molten rock into perfectly round droplets. These droplets then cooled in the vacuum of space, preserving their spherical shape as they were incorporated into asteroids.
For decades, scientists struggled to explain how chondrules got their characteristic round shape and specific cooling rates. Previous theories required very specific, unlikely conditions to work. But this new model shows that chondrule formation happened naturally during the most dramatic period of Jupiter's growth, when the giant planet was rapidly accumulating gas from the surrounding nebula.
The researchers developed sophisticated computer simulations that tracked Jupiter's growth and modelled how its gravity caused high speed collisions between planetesimals. When they compared their simulated chondrules to real meteorite samples, the match was remarkable. The model spontaneously produced droplets with the same sizes, cooling rates, and other characteristics found in actual meteorites.
486958 Arrokoth, the first pristine planetesimal visited by a spacecraft (Credit : NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko)
This discovery provides the first reliable method for dating when planets formed. The model shows that chondrule production coincides with Jupiter's intense accumulation of nebular gas to reach its massive size. Since meteorite data shows peak chondrule formation occurred 1.8 million years after the Solar System began, this pinpoints precisely when Jupiter was born.
The implications extend beyond our solar system. Chondrules of different ages found in meteorites suggest that other giant planets like Saturn also triggered similar violent processes when they formed. By studying chondrules of various ages, scientists can now trace the birth order of planets and understand how our Solar System developed over time.
Chondrules in the chondrite classification Grassland. A millimetre scale is shown.
This research also offers insights into planetary formation around other stars. The violent collisions that created chondrules likely occur in other planetary systems as giant planets form, suggesting that similar processes shape solar systems throughout the Galaxy.
What makes this discovery particularly elegant is how it connects microscopic spheres in meteorites to one of the most significant events in our Solar System's history. These "molten rock raindrops" that have survived billions of years of cosmic wandering have finally revealed their secret: they are the signature of Jupiter's birth, preserved in stone for us to discover today.
Source : Scientists Date the Origin of Jupiter by Studying the Formation of “Molten Rock Raindrops”
