West LA Times

Researchers from UCLA have found that the orbits of exoplanets differ significantly based on their size. Large planets often exhibit elliptical orbits, while smaller ones tend to have circular paths. This discovery suggests two distinct formation pathways for small and large planets.

Gregory Gilbert, a postdoctoral researcher at UCLA and lead author of the study published in the Proceedings of the National Academy of Sciences, explained, "What we found is that right around the size of Neptune, planets go from being almost always on circular orbits to very often having elliptical orbits."

The team used data from NASA's Kepler telescope, which observed 150,000 stars and detected thousands of exoplanets by measuring dips in brightness caused by transiting planets. The analysis focused on light curves to determine orbit shapes.

UCLA physics and astronomy professor Erik Petigura highlighted a challenge in modeling these light curves: "If stars behaved like boring light bulbs, this project would have been 10 times easier." He noted each star-planet system has unique characteristics that required careful examination.

UCLA undergraduate Paige Entrican contributed by creating a visualization tool kit to manually inspect each light curve. Entrican said, "Reviewing the data was a meticulous process that required careful inspection of all data products to ensure the validity of our results."

The research also aligns with other known features in exoplanet populations. As Gilbert stated, “Small planets are common; large planets are rare. Large planets need metal-rich stars in order to form; small planets do not.”

This study enhances understanding of planetary formation processes. Gilbert remarked on the significance: “To see a transition in the eccentricities of the orbits at this same point tells us there really is something very different about how these giant planets form versus how small planets like Earth form."

Petigura acknowledged Johannes Kepler's historical contributions: “It’s remarkable what we've been able to learn about the orbits of planets around other stars using the Kepler Space Telescope.” He added that Kepler would likely be pleased with these advancements.