Figuring out what happened in the solar system thousands or hundreds of millions of years ago is challenging. Millions of objects of vastly different masses interacted for billions of years, seeking natural stability. But its history, including the migration of giant planets, explains what we see today in our solar system and in other distant solar systems.
New research shows that giant planet migration began soon after the formation of the solar system.
Planetary migration is a well-established idea. The Great Course Hypothesis holds that Jupiter formed at 3.5 AU, migrated inward to 1.5 AU, and then returned again to 5.2 AU, where it is today. Saturn is also involved. Migration could also explain the hot Jupiters we see orbiting very close to stars in other solar systems. They couldn’t have formed there, so they must have migrated there. Even rocky planets could migrate early in the solar system’s history.
New research in the journal Science pinpoints the date of migration of the solar system’s giant planets. It is titled “Dating Orbital Instabilities of the Solar System’s Giant Planets Using Enstatite Meteorites.” The lead author is Dr Chrysa Avdellidou from the School of Physics and Astronomy at the University of Leicester.
“The question is, when did this happen?” Dr. Avdridu asked. “Due to some dynamical process, the orbits of these planets became unstable and then reached the final position we see today. Each timing has a different meaning, which has been a source of debate in the community.
“What we tried to do in this work was not just to do purely dynamical studies, but to combine different types of studies, linking observations, dynamical simulations and meteorite studies.”
The meteorites in this study are enstatite, or E-type asteroids. E-type asteroids have enstatite (MgSiO3) achondrite surfaces. Achondrites mean that they lack chondrules, grains of rock that were once melted before accreting into their parent body. Specifically, this group of meteorites are low-iron chondrites called ELs.
When the giant planets move, everything else reacts. Tiny asteroids are insignificant compared to the mass of Jupiter. Scientists believe that E-type asteroids were dispersed during the outward migration of gas giant planets. They may even have been the impactors of the supposed late heavy bombardment.
Enstatite achondrites that hit Earth have compositions and isotope ratios similar to those of Earth. This suggests that they formed in the same part of the protoplanetary disk around the young Sun. Previous research by Dr. Avdellidu and others has linked these meteorites to a debris group in the asteroid belt called Atsol.
Key to this work is linking the meteorite to the parent asteroid and measuring the isotope ratios.
“If meteorite types can be linked to a specific parent asteroid, it could provide insight into the asteroid’s composition, formation time, temperature evolution and original size,” the authors explain. Isotope abundance is particularly important when it comes to composition. Different isotopes decay at different rates, so analyzing their ratios can tell researchers when each meteorite closed in, that is, when it became cold enough that the isotopes no longer diffuse significantly. “Thermometers in meteorites could therefore limit the times when major impact events disrupted the parent asteroid’s cooling curve,” the authors explain.
The team’s research shows that Attor was part of a once larger parent body that formed much closer to the sun. It also suffered a collision that shrank its size beyond the asteroid belt.
When the giant planets migrated, Athol found his way back. Atsol was at the mercy of all the moving mass and underwent its own migration back to the asteroid belt. Analysis of meteorites shows that this could not have happened earlier than 60 million years ago. Other studies of asteroids orbiting Jupiter suggest it could not have happened any later than 100 million years ago. Since the solar system formed about 4.56 billion years ago, giant planet migration occurred 4.5 to 4.46 billion years ago.
A shows the formation and cooling of EL parent planetesimals in the Earth-like planetary region before 60 Myr after the formation of the solar system. During this period, terrestrial planets began to disperse planetesimals into highly eccentric and semi-major axis orbits corresponding to the main belt of asteroids. B shows that EL planetesimals were destroyed by impacts in the Earth-like planetary region between 60 and 100 Myr. At least one fragment (the ancestor of the Athol family) was dispersed into a dispersed disk by an Earth-like planet, as shown in (A). The instability of the giant planet then implants it into the inner main belt by lowering its eccentricity. C shows that tens of millions of years after the giant planet instability occurred, a huge impact occurred between the planetary embryo Theia and the proto-Earth, forming the moon. D shows that the ancestor of the Athor family experienced another impact event, forming the Athor family at about 1500 Myr. Image credit: Avdellidou et al. 2024.
Another important event occurred around the same time. About 4.5 billion years ago, a protoplanet called Theia struck the Earth and created the moon. Could it all be related?
“Moon formation also occurred within the range of instabilities we identified for giant planets,” the authors wrote in their study. “It could be a coincidence or there could be a causal relationship between the two things.”
“It’s like you have a puzzle where you know something is supposed to happen, and then you try to put the events in the right order to form the picture you see today,” Dr. Avdridu said. “The novelty of this study is that we don’t just do purely dynamical simulations, or just experiments, or just telescopic observations.”
“Our solar system once had five inner planets instead of four, so that could have implications for other things, like how we formed habitable planets. Questions like when exactly did objects deliver volatiles and organics to Our planet, Earth and Mars?
The history of the solar system is an intricate, beautiful puzzle that has somehow led us to it. Everything had to go smoothly for life to emerge on Earth, sustain itself, and evolve for so long. The epic migration of gas giants certainly plays a role, and this study puts its role in the spotlight.
Regardless of habitability, complex life and civilization, migration may have allowed the Earth to form in the first place.
“The timing is very important because our solar system was filled with a huge number of planetesimals from the beginning,” said study co-author Marco Delbo, director of research at the Nice Observatory in France. “Instabilities will clear them out, so if this happens 10 million years after the start of the solar system, you’ll clear out the planetesimals immediately, whereas if you do it 60 million years later, you’ll have more time to bring matter with you. To Earth and Mars.
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