View larger. | Artist’s concept of an Earth-sized exoplanet, in this case LP 791-18 d, some 90 light-years away. Evidence suggests it’s a volcano-covered world, perhaps as active as Jupiter’s moon Io. So, what is a planet? Image via NASA/ Goddard Space Flight Center/ Chris Smith (KRBwyle).
On Monday, July 22, 2024, EarthSky’s Deborah Byrd will speak LIVE with Jean-Luc Margot, a Belgian-born astronomer and UCLA professor. Margot and his team just published a new study, outlining the reason we need a new definition of “planet.” They will present their ideas to the IAU General Assembly – a global meeting of astronomers – beginning on August 6 in Cape Town, South Africa.
When Pluto was demoted from full planet status in 2006, it was because the International Astronomical Union’s definition of a planet had changed. The change created an uproar. But, since the mid-1990s, scientists have discovered more than 5,000 exoplanets, or worlds orbiting distant stars. Meanwhile, the IAU definition applies only to planets within our solar system. The newly proposed planet definition is less sun-centric.
The new definition specifies that “planets” may orbit one or more stars, brown dwarfs or stellar remnants.
It sets mass limits that its originators say should apply to planets everywhere.
But does it return Pluto to full planet status?
Jean-Luc Margot and team published a new study in The Planetary Science Journal this past week (July 17, 2024) outlining their reasons for the suggested change in the definition to “planet.” Find their study here: Quantitative Criteria for Defining Planets.
Jean-Luc Margot is a Belgian-born astronomer and UCLA professor. He obtained a B.S. in electrical engineering from the University of Louvain (1993) and a Ph.D. in astronomy from Cornell University (1999). His research interests include the dynamics and geophysics of planetary bodies, radio and radar astronomy, and SETI. Image via The Planetary Society/ Jean-Luc Margot. Used with permission.
Bottom line: When the International Astronomical Union created a definition for “planet” in 2006, Pluto lost full planet status. Now astronomers are proposing a new definition of “planet.”
Deborah Byrd
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About the Author:
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.
