The search for planets orbiting other stars in our galaxy has revealed an extraordinary family of planets whose orbits are so carefully timed that they provide long-term stability for their planetary system. A paper describing the formation of this planetary system by a research team that includes a Penn State University astrophysicist will be published in the journal Nature on May 11, 2016.
“The Kepler-223 planetary system has unusually long-term stability because its four planets interact gravitationally to keep the beat of a carefully choreographed dance as they orbit their host star,” said Eric Ford, a professor of astronomy and astrophysics at Penn State and a member of the research team. Each time the innermost planet (Kepler-223b) orbits the system’s star 3 times, the second-closest planet (Kepler-223c) orbits precisely 4 times. Thus, these two planets return to the same positions relative to each other and their host star.
Throughout the Kepler-233 system, the dance is much more elaborate. “The orbital periods of the four planets of the Kepler-233 system have ratios of exactly 3 to 4, 4 to 6, and 6 to 8,” Ford said. The ratio of the orbits of the four planets is so precise that they provide a stabilizing influence for the planetary system. “The precisely timed orbits of these planets places strong constraints on how they could have formed,” Ford said.
“Our analysis shows that a slow, smooth, migration of the system during its formation and evolution would be able to place these planets into the delicately balanced configuration that we observe today.” An example closer to home on Earth is the synchronization that a side-by-side group of undisturbed mechanical metronomes achieve over time, even though they each begin ticking at a different frequency. “The Kepler-223 system is one of the best examples of a system that provides such strong clues about how its planets could have formed,” Ford said.
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