What is it about?
Studying the orbits of thousands of exoplanets shows that large planets tend to have eccentric (elliptical) orbits, while smaller planets tend to have more circular orbits. Larger planets with eccentric orbits may have experienced a chaotic period of formation, during which planets interact via gravitational forces to produce noncircular orbits.
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Photo by NASA Hubble Space Telescope on Unsplash
Why is it important?
The eccentricity split coincides with several other classic features in the exoplanet population, such as the high abundance of small planets over large planets and a tendency for giant planets to only form around stars enriched in heavy elements such as oxygen, carbon and iron. The finding points toward two distinct pathways for forming small and large planets.
Perspectives
Our research used data collected by NASA’s Kepler telescope, which monitored 150,000 stars for four years and discovered thousands of exoplanets. Four centuries ago, Johannes Kepler (for whom the telescope is named) was the first scientist to appreciate that the planets in our solar system move on slightly elliptical rather than circular orbits. His discovery was an important moment in human history because it showed that the sun, rather than the Earth, was at the center of the solar system. Our new results thus contribute to a long tradition in astronomy of studying the shape of planetary orbits to understand our place in the universe.
Gregory Gilbert
University of California Los Angeles
Read the Original
This page is a summary of: Planets larger than Neptune have elevated eccentricities, Proceedings of the National Academy of Sciences, March 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2405295122.
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