Today, there are 5,197 confirmed exoplanets in 3,888 planetary systems, and 8,992 candidates pending confirmation. Most were massive planets with radii around 2.5 times Earth’s, ranging from Jupiter to Neptune-sized gas giants in particular. Another statistically significant population are the rocky planets (called “super-Earths”) with approximately 1.4 Earth radii.

This is a mystery to astronomers, especially when it comes to exoplanets discovered by the venerable Kepler Space Telescope. Among the more than 2,600 planets discovered by Kepler, there is an obvious rarity of exoplanets with a radius of about 1.8 times the Earth, which they refer to as the “radius valley”. The second puzzle, known as “peas in a pod”, concerns similarly sized nearby planets found in hundreds of planetary systems with harmonic orbits. In research led by the Cycles of Life-Elementary Volatile Elements project in the Rocky Planets (CLEVER) project at Rice University, an international team of astrophysics proposes a new model that explains the interaction of forces acting on newborn planets that could explain these two mysteries.

The research was led by Andre Isidoro, a postdoctoral fellow in the NASA-funded Rice CLEVER Planets project. He was joined by CLEVER Planets researchers Rajdeep Dasgupta and Andrea Isella, Hilke Schlichting of the University of California, Los Angeles (UCLA), and Christian Zimmerman and Bertram Bitch of the Max Planck Institute for Astronomy (MPIA).

As they explain in their recently published research paper Astrophysical Journal LettersThe team used a supercomputer to run a planetary migration model simulating the first 50 million years of planetary system evolution. In their models, protoplanetary disks of gas and dust also interact with the migrating planets, bringing them closer to their parent stars and locking them into resonant orbital chains. Over millions of years, the preplanetary disk disappears, breaking the chains and causing orbital instabilities that cause two or more planets to collide. While planetary migration models have been used to study planetary systems that maintain orbital resonance, these findings are a first for astronomers.

As Isidoro said in a Rice University statement: “I believe we are the first to explain the radius valley using a model of planet formation and dynamic evolution that takes into account multiple observation constraints in a self-consistent manner. “We can also show that a pattern of planet formation involving giant collisions is consistent with the ‘pea-in-a-pea’ feature of exoplanets.

This work builds on previous work by Isidoro and the CLEVER Planets project. Last year, they used a migration model to calculate the maximum destruction of the seven-planet system TRAPPIST-1. In the article published on November 21, 2021 Nature Astronomyused N-body simulations to show how the pea system in this pod can maintain its harmonic orbital structure in the face of collisions caused by migrating planets. This allowed them to impose restrictions on the upper limit of collisions and the mass of the objects involved. Their results show that the collision in the TRAPPIST-1 system is comparable to the collision that created the Earth-Moon system.

Isidoro said: “The migration of young planets to their host stars causes overcrowding and often leads to catastrophic collisions that destroy the planets’ hydrogen-rich atmospheres.

“This means that giant collisions such as those that formed our Moon were likely a common result of planet formation.”

This latest study shows that planets come in two varieties, dry and rocky planets 50 percent larger than Earth (super-Earths) and water-ice-rich planets (mini-Neptunes) about 2.5 times Earth’s size. In addition, they suggest that some of the planets twice the size of Earth will retain their original hydrogen-rich atmospheres and be rich in water. According to Isidoro, these results are consistent with new observations suggesting that super-Earths and mini-Neptunes are not just dry and rocky planets.

These findings open up opportunities for exoplanet researchers who will rely on the James Webb Space Telescope to make detailed observations of exoplanet systems. Using an advanced array of optics, infrared imaging, coronagraphs and spectrometers, Webb and other next-generation telescopes will characterize the atmospheres and surfaces of exoplanets like never before. Source