First-ever recorded planetary engulfment event captured by Webb

It was once thought that when an aging star engulfed a planet it would be a dramatic swelling and devouring event akin to a predator eating its prey. New observations, however, tell a very different story.

Data from NASA’s James Webb Space Telescope (JWST) reveals that the planet’s orbit didn’t terminate with a sudden engulfment. Instead, the planet spiraled slowly inward over time until it met its fiery end.

The scientists behind this surprising update are from NSF’s NOIRLab, and they worked with data collected by Webb’s powerful mid- and near-infrared instruments.

Their observations challenge earlier theories and offer a clearer picture of what may await planetary systems like our own.

Disappearing planet grabbed attention

The star at the center of this event sits about 12,000 light-years from Earth in our Milky Way galaxy. A flash of visible light, first spotted in 2020 and labeled ZTF SLRN-2020, originally caught astronomers’ attention.

But even earlier, infrared data from NASA’s NEOWISE mission had picked up a brightening signal that hinted at a build-up of dust.

A deeper investigation in 2023 led researchers to think the star was becoming a red giant.

Webb’s Mid-Infrared Instrument (MIRI) changed the narrative. Its ability to isolate faint emissions in crowded star fields showed that the star wasn’t as bright as a red giant should be.

In fact, it never expanded enough to swallow a planet whole.

“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.

“With its high-resolution look in the infrared, we are learning valuable insights about the final fates of planetary systems, possibly including our own.”

Engulfed planet’s final orbit

Instead of being engulfed in a sudden flash, the planet met its end in slow motion.

Researchers now believe the planet was roughly the size of Jupiter and orbited its host star much closer than Mercury orbits the Sun.

Over millions of years, it spiraled inward. Eventually, it began brushing the star’s outer atmosphere. That contact triggered a runaway effect – the closer the planet got, the faster it fell in.

“The planet, as it’s falling in, started to sort of smear around the star,” said Morgan MacLeod.

This violent encounter would have blown gas outward from the star’s surface. That gas then cooled and formed dust, creating a faint halo that continued to glow in the infrared long after the planet’s demise.

Engulfed planet leaves gas disk behind

Webb’s Near-Infrared Spectrograph (NIRSpec) offered an even closer look.

Along with the expected cool dust cloud, it revealed something much more surprising: a hot, molecular gas disk surrounding the star.

This accretion disk contained carbon monoxide and other compounds – the kind often found in regions where planets are born.

“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.

“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.”

This leftover material provides fresh clues about what happens after a planet disappears into a star.

Researchers are now questioning how the interaction may have altered the star’s outer layers or affected nearby planetary debris.

Why does any of this matter?

The event was observed under Webb’s Guaranteed Time Observation program 1240, one of the first Target of Opportunity programs ever conducted by the telescope.

These programs are meant to catch rare moments, like stellar explosions or dramatic system changes, even though scientists can’t predict exactly when or where they’ll happen.

“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,” enthused Lau. “We hope this is just the start of our sample.”

Will planet Earth be engulfed by the Sun

The Sun, like all stars, won’t shine forever. In about five to seven billion years, it’ll run out of hydrogen – the fuel that’s kept it stable and warm all this time.

When that happens, its core will contract and heat up, while the outer layers expand. The Sun will swell into a red giant, growing so massive that it might swallow Mercury and Venus.

Earth sits right on the edge of that danger zone. Some scientists think the Sun could completely engulf it. Others believe Earth might just escape, pushed outward as the Sun loses mass. Either way, the outcome isn’t good.

Even if Earth avoids getting swallowed, it won’t survive the heat. The oceans will boil away. The atmosphere will vanish. The surface will burn.

Eventually, the Sun will shed its outer layers and collapse into a tiny, dense white dwarf. What’s left of Earth – if anything – will be a frozen, lifeless husk orbiting a dim, burnt-out star. No fire, no light, no life. Just silence.

What happens next?

More events like ZTF SLRN-2020 are expected to be discovered in the future, thanks to observatories like the upcoming Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope.

These tools will scan the sky repeatedly, helping scientists to track sudden changes and expand our understanding of how stars and planets interact in their final acts.

The full study was published in the journal The Astrophysical Journal.

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