A presented a recent study at the National Astronomy Meeting 2023 (NAM2023) examines a newly discovered theory of planet formation that challenges previous ideas about how planets form in the disks of gas and dust surrounding young stars, also known as protoplanetary disks. As well as being presented at NAM2023, the research has also been submitted for peer review in the journal Monthly Notices of the Royal Astronomical Society and has the potential to help scientists better understand not only how planets form, but also how life can form on them as well.
Based on observational data and models, the researchers found that two large protoplanets—planets still forming from the accretion of dust in the disk, also known as accretion—orbiting at an undetermined distance from each other could create a smaller planet orbiting between them, which researchers call “sandwich planet formation.”
The researchers say this is because the two larger planets limit the amount of dust that flows into the inner parts of the protoplanetary disk, as both will continue to collect it. When this happens, any planet that forms between them will be smaller than the two larger planets, analogous to the filling inside a sandwich.
“This is very different from the conventional view of planet formation, where we usually expect planets to form sequentially from the inner to the outer part of the disc and become increasingly massive further out,” Dr. Farzana Meru, who is Associate Professor and Dorothy Hodgkin Fellow in the Department of Physics at the University of Warwick, said in statement. “What’s also really interesting is that there are examples that we’ve found from observations of exoplanets that actually show this planet sandwich architecture — where the average planet is less massive than its neighbors; it is also a reasonable part of the systems.
Exponent of the new “sandwich planet formation” theory considered for this study. (Courtesy of: University of Warwick/Mark A. Garlick; License Type: Attribution (CC BY 4.0))
Further studies are needed to better understand this new formation process, but it could lead to the development of plausible explanations for the existence of Mars and Uranus, which are both smaller planets orbiting between larger planets in our own solar system. In the case of Mars, the larger Earth orbits inward, while the much larger Jupiter orbits outward. In the case of Uranus, the much larger Saturn orbits inward, while the similar-sized Neptune orbits outward. While the radius of Uranus is greater than that of Neptune, the mass of the former is less, and this is due to The density of Neptune is approximately 30 percent larger than Uranus.
The planets of our solar system and their relative sizes to each other. Credit: NASA/Lunar and Planetary Institute
The current state of our solar system consists of a (mostly) clean and organized collection of planets, moons, asteroids, and comets. This includes the Sun at the center, followed by the inner planets, the asteroid belt, the outer planets, the Kuiper belt, and the Oort cloud, but things were much different approximately 4.6 billion years ago.
That was when scientists hypothesize a massive cloud of gas and dust collapsed from the shock wave of a nearby supernova and formed into a solar nebula, which consists of a rotating disk of gas and dust. As this disk spins, gravity begins to take over and continues to pull material toward the center of the disk, eventually forming our Sun, which contains 99 percent of the entire mass of the solar system, and a protoplanetary disk is born.
Over millions of years, the terrestrial planets of the inner Solar System and the large gas giants of the outer Solar System—along with their many moons—formed from the accretion of gas and dust throughout the disk. This includes Mars, which is likely to be triangulated by Earth and Jupiter, and Uranus is likely to be triangulated by Saturn and Neptune. The remaining gas and dust formed the asteroids and comets that make up the asteroid belt, the Kuiper belt, and the Oort cloud.
What new discoveries will scientists make about protoplanetary disks and “sandwich planet formation” in the coming years and decades? Only time will tell and that’s why we science!