Planetary systems such as our Solar System take hundreds of millions of years to evolve. Since humanity has only existed for a sliver of that time, astronomers have only observed planetary systems at birth or, more often, long after they have settled into adulthood. There is an information gap about what happens in the middle.
But soon, this understanding will change. For the first time, astronomers can characterize the teenage planetary system TOI-2076 in detail since its discovery in 2020. The system, spotted mid-transition, offers a novel lens into the once-mysterious evolutionary stage.
“An Adolescent, Near-Resonant Planetary System Near the End of Photoevaporation,” published in Nature Astronomy, observes and models potential markers of cosmic adolescence using key evidence: the separation of a once tightly packed planetary system and the dynamic evaporation of planets’ atmospheres caused by intense stellar radiation.
Florida Tech assistant professor Howard Chen, who uses computer models to illustrate and estimate planetary evolution, co-authored the paper with a global group of researchers (including astronomers at California Institute of Technology, University of Hawaii and Nanjing University) to test his models’ ability to match this system’s outcome from simulated origins. His calculations provide strong insight into the short-lived shift from planetary youth to maturity across the universe.
“The transformative period is so short compared to the entire lifespan of the system,” Chen said. “That period is really the key in determining how it turns out at its mature state.”
The system’s four planets orbit a youthful K-dwarf star – at “just” 210 million years old, an adolescent by cosmic standards. Using ground-based telescopes and data from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, the scientists found that the planets are spaced with a nearly consistent orbital sequence, indicating they were once tightly packed but are slowly spreading apart. They also found that the planets all share similar rocky cores with a range of different atmospheres: the innermost planet completely shed its original gases, while the outer three retained their atmospheres.
Chen predicted that the gradual shedding of birth atmospheres was driven by a process called photoevaporation. This occurs when powerful radiation from an energy source, such as a star, heats a planet’s atmosphere until gas escapes into space. Planets that are closer to the star and thus receive higher amounts of radiation would lose more gas and be left with more rock than their farther counterparts.
He decided to use his existing evolution models to simulate how photoevaporation would shape the evolution of similar planets from origin to adolescence, all born with the same initial rock-to-gas composition. Would his simulation yield the same result that was observed in real life?
Yes. In his simulation, Chen found that the planets naturally evolved into a state similar to the actual system’s observed state. Therefore, he could assume that photoevaporation was at play; radiation from the system’s star is what stripped some planets into bare rocks while leaving others with a gaseous atmosphere. The models also indicated that planet mass, which changes with gas loss, contributed to the gradual distancing of planets in an orbital sequence.
As someone who primarily works with theoretical models, Chen is thrilled that his simulations matched the observed reality.
“For me, the whole point of going into modeling is to be able to connect with observations. You want your models to say something about the real world, but that’s not necessarily the case every time,” he said. “To see the model work in the real world and explain what’s happening is pretty powerful.”
The simulation also delivered an approximate timeline for how long it takes a system to reach adolescence, suggesting that most atmosphere loss happens within the first 100 million years of a system’s life. After that point, the system’s formation stabilizes and remains as is for billions of years.
Chen’s model, now updated with these new findings, will help astronomers unpack the histories of older planetary systems. It can also guide predictions of how the young planets they’ve discovered will eventually evolve.
Catching TOI-2076 mid-evolution was a rare feat that yields extremely valuable findings. Understanding when a planetary system hits its transformational teenage years – and what that looks like – provides a critical snapshot of how infant systems evolve and settle into the stable configurations observed around older stars. The new link will help illustrate a clearer picture of how planetary systems, including those like our own, grow up.
