Today the number of confirmed exoplanets is 5,197 in 3,888 planetary systems, with another 8,992 candidates awaiting confirmation. The majority were particularly massive planets, ranging from gas giants the size of Jupiter and Neptune, with radii about 2.5 times Earth’s radius. Another statistically significant population were rocky planets measuring about 1.4 Earth radii (“super-earths”). This baffles astronomers, especially when it comes to the exoplanets discovered by the venerable Kepler space telescope.
Of the more than 2,600 planets Kepler discovered there is an apparent rarity of exoplanets with a radius of about 1.8 times Earth’s radius – which they refer to as “Radius Valley”. A second mystery, known as “peas in a pod,” relates to similar-sized neighboring planets found in hundreds of planetary systems with harmonic orbits. In a study led by the Cycles of Life-Essential Volatile Elements in Rocky Planets (CLEVER) project at Rice University, an international team of astrophysicists proposes a new model that considers the interplay of forces acting on newborn planets and their birth could explain both mysteries .
The research was led by André Izidoro, a Welch Postdoctoral Fellow at Rice’s NASA-funded CLEVER Planets project. He was joined by fellow researchers from CLEVER Planets, Rajdeep Dasgupta and Andrea Isella, Hilke Schlichting from the University of California, Los Angeles (UCLA), and Christian Zimmermann and Bertram Bitsch from the Max Planck Institute for Astronomy (MPIA). As they describe in their research recently published in the Astrophysical Journal Lettersthe team used a supercomputer to run a planetary migration model that simulated the first 50 million years of planetary system evolution.
In their model, protoplanetary disks of gas and dust also interact with wandering planets, pulling them closer to their parent stars and trapping them in resonant orbital chains. Within a few million years, the protoplanetary disk disappears, breaking 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 have retained orbital resonances, these results represent a first for astronomers. As Izidoro said in a Rice University statement:
“I believe we are the first to explain Radius Valley with a model of planet formation and dynamic evolution that self-consistently accounts for several observational limitations. We can also show that a planet formation model involving giant impacts is consistent with the pea-in-a-pod property of exoplanets.”
This work builds on previous work by Izidoro and the CLEVER Planets project. Last year they used a migration model to calculate the maximum perturbation of TRAPPIST-1’s seven-planet system. In a paper published in November 21, 2021 natural astronomy, they used an N-body simulation to show how this peas-in-a-pod system could have maintained its harmonic orbital structure despite collisions caused by planetary migration. This allowed them to set constraints on the upper limit of collisions and the masses of the objects involved.
Their results show that collisions in the TRAPPIST-1 system were comparable to the impact that created the Earth-Moon system. Said Izidoro:
“The migration of young planets to their host stars causes overcrowding and often results in catastrophic collisions that strip the planets of their hydrogen-rich atmospheres. That means giant impacts like the one that formed our moon are likely a generic result of planet formation.”
This latest research suggests there are two varieties of planets, consisting of arid and rocky planets that are 50 percent larger than Earth (super-Earths) and planets that are rich in water ice, about 2.5 times larger big as the earth (mini Neptune). In addition, they suggest that a fraction of planets twice the size of Earth will retain their original hydrogen-rich atmospheres and be watery. According to Izidoro, these results are consistent with new observations suggesting that super-Earths and mini-Neptunes are not exclusively dry and rocky planets.
These results provide opportunities for exoplanet researchers who will rely on the James Webb Space Telescope to make detailed observations of exoplanet systems. With its advanced suite of optics, infrared imaging, coronagraphs and spectrometers, Webb and other next-generation telescopes will characterize the atmospheres and surfaces of exoplanets like never before.
This article was originally published on universe today by Matt Williams. Read the original article here.
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