The James Webb Space Telescope’s MIRI instrument has captured the final moments of a planet’s existence, unexpectedly revealing that the object descended into its host star rather than being engulfed by it as it grew.
NASA believes this is the first time a star swallowing a planet has been directly observed, an important moment for astrophysics. Defying earlier hypotheses, the planet’s orbit continually shrank during the recent observations, with astronomers watching as it drew closer to its fiery demise.
It Began with a Flash
The star is a subluminous red nova (SLRN) known as ZTF SLRN-2020, located 12,000 light years from Earth in the Milky Way Galaxy. Astronomers first detected it as a brilliant optical flash from the Zwicky Transient Facility (ZTF) at Caltech’s Palomar Observatory in San Diego, California.
In 2023, scientists used NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) to examine the star. The NEOWISE identified increased infrared brightness a year preceding the flash, suggesting dust in the region. From this data, astronomers hypothesized the star was similar to Earth’s sun and hundreds of thousands of years into burning out its hydrogen fuel while expanding into a red giant.
James Webb Space Telescope Observes the Death of a Planet
Among the four instruments aboard the James Webb Space Telescope (JWST), MIRI (Mid-Infrared Instrument) and NIRSpec (Near-Infrared Spectrograph) proved particularly useful in understanding the cosmic collision.
“Because this is such a novel event, we didn’t quite know what to expect when we decided to point this telescope in its direction,” said Ryan Lau, lead author of the new paper and astronomer at NSF NOIRLab (National Science Foundation National Optical-Infrared Astronomy Research Laboratory) in Tucson, Arizona. “With its high-resolution look in the infrared, we are learning valuable insights about the final fates of planetary systems, possibly including our own.”
However, the MIRI data soon turned the expanding red giant assumption on its head. The instrument’s high resolution and sensitivity revealed much more precisely what was occurring with the star and its surroundings through a congested region of space. It turned out that the star was dimmer than expected and not swelling to consume its planetary meal as scientists had surmised.
An Ever-Tightening Circle
The team believes the former planet was roughly similar to Jupiter’s size, yet held an orbit hugging its star even tighter than Mercury in our solar system. It took millions of years, but eventually, the planet came too close to its host star for comfort.
“The planet eventually started to graze the star’s atmosphere. Then it was a runaway process of falling in faster from that moment,” said team member Morgan MacLeod of the Harvard-Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology in Cambridge, Massachusetts. “The planet, as it’s falling in, started to sort of smear around the star.”
Gas Holds Clues to Planetary Riddles
Gas would have erupted off of the star as the planet impacted, eventually cooling into the dust cloud observed within a year. Such a dust cloud was expected even in the astronomer’s earlier expanding red giant theory. Yet, scientists had to reconsider their theory when NIRSpec observed a hot circumstellar disk of molecular gas near the star, and spectral imaging found carbon monoxide within the accretion, providing clues for their final hypothesis.
“With such a transformative telescope like Webb, it was hard for me to have any expectations of what we’d find in the immediate surroundings of the star,” said Colette Salyk of Vassar College in Poughkeepsie, New York, an exoplanet researcher and co-author on the new paper.
“I will say, I could not have expected seeing what has the characteristics of a planet-forming region, even though planets are not forming here, in the aftermath of an engulfment,” Salyk added.
Resolving the nature of the gas aids scientists as they reconstruct the planet’s final moments.
“This is truly the precipice of studying these events. This is the only one we’ve observed in action, and this is the best detection of the aftermath after things have settled back down,” Lau said. “We hope this is just the start of our sample.”
The paper “Revealing a Main-sequence Star that Consumed a Planet with JWST” appeared on April 10, 2025, in The Astrophysical Journal.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.