Webb Captures a Planet’s Final Plunge Into Its Star – And It Wasn’t What Scientists Expected

Lingering Brightness Provides Evidence for How the Planet Met Its Demise

Each year, scientists from around the world compete for a chance to use NASA’s James Webb Space Telescope. Proposals go through a rigorous review process, and approved projects are added to Webb’s observation schedule, which is carefully planned based on factors like timing and visibility.

But what happens when astronomers want to study something unpredictable — like a supernova or a gamma ray burst — without knowing exactly when or where it will happen? That’s where a special type of observation comes in, known as a Target of Opportunity (ToO). These observations are proposed in advance, so they’re ready to activate when the right event occurs.

One of Webb’s first ToO programs has now paid off, offering rare insights into what happens just after a star consumes one of its own planets.

Webb Space Telescope’s Autopsy of Planet Swallowed by Star Yields Surprise

NASA’s James Webb Space Telescope has revealed a surprising twist in what was thought to be the first direct observation of a star swallowing a planet. Earlier theories suggested the star had expanded into a red giant, eventually engulfing the nearby planet. But new Webb data tells a different story: instead of the star growing, the planet’s orbit gradually shrank over time — spiraling inward until it was ultimately consumed.

“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.”

To investigate what happened, scientists used two of Webb’s powerful instruments: MIRI (the Mid-Infrared Instrument) and NIRSpec (the Near-Infrared Spectrograph). Together, these tools provided a detailed look at the aftermath, allowing researchers to piece together how the planet met its end.

A Star 12,000 Light-Years Away

The star at the center of this scene is located in the Milky Way galaxy about 12,000 light-years away from Earth.

The brightening event, formally called ZTF SLRN-2020, was originally spotted as a flash of optical light using the Zwicky Transient Facility at Caltech’s Palomar Observatory in San Diego, California. Data from NASA’s NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) showed the star actually brightened in the infrared a year before the optical light flash, hinting at the presence of dust. This initial 2023 investigation led researchers to believe that the star was more Sun-like, and had been in the process of aging into a red giant over hundreds of thousands of years, slowly expanding as it exhausted its hydrogen fuel.

However, Webb’s MIRI told a different story. With powerful sensitivity and spatial resolution, Webb was able to precisely measure the hidden emission from the star and its immediate surroundings, which lie in a very crowded region of space. The researchers found the star was not as bright as it should have been if it had evolved into a red giant, indicating there was no swelling to engulf the planet as once thought.

How the Planet Was Consumed

Researchers suggest that, at one point, the planet was about Jupiter-sized but orbited quite close to the star, even closer than Mercury’s orbit around our Sun. Over millions of years, the planet orbited closer and closer to the star, leading to the catastrophic consequence.

“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.”

In its final splashdown, the planet would have blasted gas away from the outer layers of the star. As it expanded and cooled off, the heavy elements in this gas condensed into cold dust over the next year.

Inside the Aftermath

While the researchers did expect an expanding cloud of cooler dust around the star, a look with the powerful NIRSpec revealed a hot circumstellar disk of molecular gas closer in. Furthermore, Webb’s high spectral resolution was able to detect certain molecules in this accretion disk, including carbon monoxide.

“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.”

Still More Questions Than Answers

The ability to characterize this gas opens more questions for researchers about what actually happened once the planet was fully swallowed by the star.

“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.”

Catching the Next Cosmic Catastrophe

These observations, taken under Guaranteed Time Observation program 1240, which was specifically designed to investigate a family of mysterious, sudden, infrared brightening events, were among the first Target of Opportunity programs performed by Webb. These types of study are reserved for events, like supernova explosions, that are expected to occur, but researchers don’t exactly know when or where. NASA’s space telescopes are part of a growing, international network that stands ready to witness these fleeting changes, to help us understand how the universe works.

Eyes on the Sky for Future Events

Researchers expect to add to their sample and identify future events like this using the upcoming Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope, which will survey large areas of the sky repeatedly to look for changes over time.

The team’s findings were published on April 10, in The Astrophysical Journal.

Reference: “Revealing a Main-sequence Star that Consumed a Planet with JWST” by Ryan M. Lau, Jacob E. Jencson, Colette Salyk, Kishalay De, Ori D. Fox, Matthew J. Hankins, Mansi M. Kasliwal, Charles D. Keyes, Morgan Macleod, Michael E. Ressler and Sam Rose, 10 April 2025, The Astrophysical Journal.
DOI: 10.3847/1538-4357/adb429

More About JWST and MIRI

The James Webb Space Telescope (JWST) is the world’s leading space science observatory, designed to explore everything from planets in our solar system to the most distant galaxies in the universe. A collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), Webb is helping scientists uncover the origins of stars, galaxies, and planetary systems—including clues about our own place in the cosmos.

One of Webb’s most powerful instruments is MIRI (the Mid-Infrared Instrument), developed through a 50-50 partnership between NASA and ESA. MIRI allows astronomers to see the universe in mid-infrared light, revealing cool objects like forming planets, distant galaxies, and dusty cosmic environments. The U.S. side of the project was led by NASA’s Jet Propulsion Laboratory (JPL), with key contributions from Caltech and Northrop Grumman. George Rieke of the University of Arizona leads the MIRI science team, while Gillian Wright serves as the European principal investigator. The critical MIRI cryocooler, which keeps the instrument cold enough to detect faint heat signals, was developed by JPL in collaboration with NASA Goddard and Northrop Grumman.

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