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JWST postmortem of planet ‘eaten’ by star yields surprise

Back in 2020, a planet was believed to have been swallowed by a star becoming a red giant, the latest findings by NASA’a James Webb Space Telescope (JWST) however yielded surprising results

Saturday April 12, 2025 6:05 PM, Science Desk

[NASA’s James Webb Space Telescope’s observations of what is thought to be the first-ever recorded planetary engulfment event revealed a hot accretion disk surrounding the star, with an expanding cloud of cooler dust enveloping the scene. NASA, ESA, CSA, R. Crawford (STScI)]

Back in 2020, a planet was believed to have been swallowed by a star becoming a red giant, the latest findings by NASA’a James Webb Space Telescope (JWST) however yielded surprising results.

“The new findings suggest that the star actually did not swell to envelop a planet as previously hypothesized. Instead, Webb’s observations show the planet’s orbit shrank over time, slowly bringing the planet closer to its demise until it was engulfed in full”, NASA Webb Mission Team said in a blog post.

A study three years later suggested that ZTF SLRN-2020 was a red giant—an older star that had expanded in size and that it had swallowed a gas giant planet orbiting around it.

According to the 2023 study, the bright flash came from the planet being destroyed inside the red giant’s outer layers. The leftover dust, created as the planet burned up, was thought to be the source of the infrared glow picked up by NEOWISE.

Located in Milky Way, the planet is believed to have been from a class called "hot Jupiters" — gas giants at high temperatures owing to a tight orbit around their host star.

JWST Autopsy Report

The latest finding based on, what is called as postmortem by JWST - NASA’s orbiting telescope, however reveals a totally different story.

The JWST findings indicate that the planet's demise happened differently than initially thought. Instead of the star coming to the planet, it appears the planet came to the star, with disastrous consequences — a death plunge after an erosion of this alien world's orbit over time, researchers said, as reported by news agency Reuters.

"We do know that there is a good amount of material from the star that gets expelled as the planet goes through its death plunge. The after-the-fact evidence is this dusty leftover material that was ejected from the host star," said astronomer Ryan Lau of the US National Science Foundation's NOIRLab, lead author of the study published in the Astrophysical Journal.

The researchers believe that the planet's orbit had gradually deteriorated due to its gravitational interaction with the star, and hypothesized about what happened next.

"Then it starts grazing through the atmosphere of the star. At that point, the headwind of smashing through the stellar atmosphere takes over and the planet falls increasingly rapidly into the star," study co-author Morgan MacLeod, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics said.

"The planet both falls inward and gets stripped of its gaseous outer layers as it plows deeper into the star. Along the way, that smashing heats up and expels stellar gas, which gives rise to the light we see and the gas, dust and molecules that now surround the star," MacLeod said.

But they cannot be certain of the actual fatal events.

"In this case, we saw how the plunge of the planet affected the star, but we don't truly know for certain what happened to the planet. In astronomy there are lots of things way too big and way too 'out there' to do experiments on. We can't go to the lab and smash a star and planet together - that would be diabolical. But we can try to reconstruct what happened in computer models," MacLeod said.

None of our solar system's planets are close enough to the sun for their orbits to decay, as happened here. That does not mean that the sun will not eventually swallow any of them.

About five billion years from now, the sun is expected to expand outward in its red giant phase and could well engulf the innermost planets Mercury and Venus, and maybe even Earth. During this phase, a star blows off its outer layers, leaving just a core behind - a stellar remnant called a white dwarf.

Webb's new observations are giving clues about the planetary endgame.

"Our observations hint that maybe planets are more likely to meet their final fates by slowly spiraling in towards their host star instead of the star turning into a red giant to swallow them up. Our solar system seems to be relatively stable though, so we only have to worry about the sun becoming a red giant and swallowing us up," Lau said.

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