Early migration may explain the disappearance of planets


A new model that accounts for the interaction of the forces acting on newborn planets can explain puzzling observations among the 3,800 cataloged planetary systems.

A puzzle known as the “Radium Valley” refers to the rarity of exoplanets with a radius about 1.8 times that of Earth. NASA’s Kepler spacecraft observed planets of this size between 2 and 3 times smaller than super-Earths with radii about 1.4 times that of Earth and mini-Neptunes with radii about 2.5 times that of Earth.

The second mystery, known as “peas in a pod”, refers to neighboring planets of similar size that have been found in hundreds of planetary systems. These include TRAPPIST-1 and Kepler-223, which also feature planetary orbits of almost musical harmony.

“I think we are the first to explain the radius valley using a model of planet formation and dynamical evolution that consistently accounts for multiple observational limitations,” he said. it’s a statement AndrĂ© Izidoro of Rice University, corresponding author of a study published this week in Astrophysical Journal Letters. “We can also show that a model of planet formation incorporating giant impacts is consistent with the pea-in-a-pod feature of exoplanets.”

Izidoro, a Welch Postdoctoral Fellow in Rice’s NASA-funded CLEVER Planets project, and co-authors used a supercomputer to simulate the first 50 million years of the development of planetary systems using a model of planetary migration. In the model, the protoplanetary disks of gas and dust that give rise to young planets also interact with them, bringing them closer to their parent stars and locking them into resonant orbital chains. The chains break after a few million years, when the disappearance of the protoplanetary disk causes orbital instabilities that cause two or more planets to collide with each other.

Planetary migration models have been used to study planetary systems that have retained their resonant orbital chains. For example, Izidoro and colleagues at CLEVER Planets used a 2021 migration model to calculate the maximum amount of disruption TRAPPIST-1’s seven-planet system could have endured during the bombardment. and yet it retained its harmonious orbital structure.

On the new study, Izidoro teamed up with CLEVER Planets researchers Rajdeep Dasgupta and Andrea Isella, both of Rice, Hilke Schlichting of the University of California, Los Angeles, and Christian Zimmermann and Bertram Bitsch of the Max Planck Institute for Astronomy in Heidelberg. Germany.

“The migration of young planets toward their host stars creates overpopulation and frequently results in cataclysmic collisions that strip planets of their hydrogen-rich atmospheres,” Izidoro said. “That means that giant impacts, like the one that formed our moon, they are probably a generic result of planet formation.”

Research suggests that the planets come in two “flavors”, super-Earths that are dry, rocky, and 50% larger than Earth, and mini-Neptunes that are rich in water ice and about 2.5 times larger than Earth. Izidoro said the new observations appear to support the results, which conflict with the traditional view that both super-Earths and mini-Neptunes are exclusively dry, rocky worlds.

Based on their findings, the researchers made predictions that can be tested by NASA’s James Webb Space Telescope. They suggest, for example, that a fraction of planets about twice the size of Earth will retain their primordial hydrogen-rich atmosphere and be water-rich.