Early planetary migration may explain missing planets

HOUSTON – (November 7, 2022) – A new model that accounts for the interaction of forces acting on infant planets may explain two puzzling observations that have cropped up repeatedly among the more than 3,800 planetary systems cataloged to date.

A puzzle known as the “radius valley” refers to the rarity of exoplanets with a radius about 1.8 times that of Earth. NASA’s Kepler spacecraft has observed planets of this size about 2-3 times less frequently than it has observed 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 exhibit planetary orbits of near-musical harmony.

“I believe we are the first to explain the valley of the ray using a model of planet formation and dynamic evolution that consistently accounts for multiple observational constraints,” said André Izidoro of Rice University. , corresponding author of a study published this week in Astrophysical Journal. Letters. “We are also able to 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 from Rice’s NASA-funded CLEVER Planets project, and his co-authors used a supercomputer to simulate the first 50 million years of planetary system development using a migration model planetary. 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 in a few million years, when the disappearance of the protoplanetary disc causes orbital instabilities which lead two or more planets to collide.

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

In 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. astronomy in Heidelberg, Germany. .

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

The research suggests the planets come in two ‘flavors’, super-Earths that are dry, rocky and 50% larger than Earth, and mini-Neptunes rich in water ice and around 2.5 times larger than Earth. Izidoro said new observations appear to support the findings, which contradict the traditional view that 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 roughly twice the size of Earth will retain both their primordial hydrogen-rich atmosphere and be water-rich.

The research was funded by NASA (80NSSC18K0828), the Welch Foundation (C-2035-20200401), and the European Research Council (757448-PAMDORA).

Peer-reviewed article

“Exoplanet Radius Valley from Gas-Induced Planetary Migration and Resonance Chain Breaking” | Astrophysical Journal Letters | DOI: 10.3847/2041-8213/ac990d

André Izidoro, Hilke E. Schlichting, Andrea Isella, Rajdeep Dasgupta, Christian Zimmermann and Bertram Bitsch

https://doi.org/10.3847/2041-8213/ac990d

Image downloads

https://exoplanets.nasa.gov/resources/2319/exoplanet-types-illustration/
CAPTION: An illustration of the variations among more than 5,000 known exoplanets discovered since the 1990s. (Image courtesy of NASA/JPL-Caltech)

https://news-network.rice.edu/news/files/2022/10/1102_GAP-graph-lg.jpeg
CAPTION: An illustration depicting the rarity of exoplanets about 1.8 times the size of Earth that have been observed by NASA’s Kepler spacecraft. (Graphic courtesy of A. Izidoro/Rice University)

https://news-network.rice.edu/news/files/2022/11/1102_GAP-izidoro16-lg.jpg
CAPTION: André Izidoro (Photo by Jeff Fitlow/Rice University)

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