Solve the mystery of the existence of "missing" planets through space
The number of confirmed exoplanets is 5,197 in 3,888 planetary systems, with another 8,992 candidates awaiting confirmation.
The vast majority were particularly massive planets, starting with gas giants the size of Neptune and Jupiter, which have a radius of about 2.5 times that of Earth.
Another statistically significant group is the rocky planets, which measure about 1.4 Earth's radii (also known as "super-Earths").
This is a mystery to astronomers, especially when it comes to the exoplanets discovered by the Kepler space telescope.
Among the more than 2,600 planets discovered by Kepler, there is a distinct paucity of exoplanets with a radius of about 1.8 times that of Earth - referred to as the "Valley of Radius".
The second puzzle refers to neighboring planets of similar size found in hundreds of planetary systems with harmonious orbits.
In a study led by the Basic Life Cycles of Volatile Elements in Rocky Planets (Clever) project at Rice University, an international team of astrophysicists presented 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 of NASA's CLEVER Planets project. He was joined by Clever planetary researchers Rajdeep Dasgupta, Andrea Isella and Helk Schlechting from UCLA and Christian Zimmermann and Bertram Piech from the Max Planck Institute for Astronomy (MPIA).
As they describe in their paper, which recently appeared in Astrophysical Journal Letters, the team used a supercomputer to run a planetary migration model that simulates the first 50 million years of planetary system development.
In their model, protoplanetary disks of gas and dust also interact with migrating planets, drawing them close to their parent stars and trapping them in resonant orbital chains.
Within a few million years, the protoplanetary disk disappears, breaking the chains and causing orbital instabilities that cause two or more planets to collide.
In a paper appearing November 21, 2021 in Nature Astronomy, they used N-body simulations to show how a system called a "pea in a pod" can maintain its harmonious orbital structure despite collisions caused by planetary migration. This allowed them to set limits on the upper limit of the collision and the mass of the objects involved.
Their results indicate that the collisions in the TRAPPIST-1 system were comparable to the impact that created the Earth-Moon system.
“The migration of young planets towards their host stars creates overcrowding and often leads to catastrophic collisions that strip planets of their hydrogen-rich atmospheres,” Isidoro said. This means that giant impacts, like the one that shaped our moon, may be a general consequence of planet formation.”
This latest research indicates that planets come in two distinct types, consisting of dry, rocky planets 50% larger than Earth (super-Earths) and water-ice-rich planets more than 2.5 times the size of Earth (minor Neptunes).
In addition, they suggest that a small fraction of planets twice the size of Earth would retain primordial hydrogen-rich atmospheres and be rich in water.
According to Isidoro, these results are consistent with new observations that the super-Earths and minor Neptunes are not just dry and rocky planets.
These findings present opportunities for exoplanet hunters, who will rely on the James Webb Space Telescope to make detailed observations of exoplanet systems.
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