In a cosmic event 12,000 light-years away, astronomers have captured, for the first time, the dramatic death of a planet as it was swallowed by its host star—not by expansion, but by a doomed inward spiral.
Originally believed to have perished when its star ballooned into a red giant, new evidence from NASA’s James Webb Space Telescope tells a different story. According to recent observations published in the Astrophysical Journal, the planet did not wait for the star to come to it—instead, it plunged inward, its orbit eroding until it dove fatally into the star.
"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," explained Ryan Lau, lead author of the study and astronomer at the U.S. National Science Foundation’s NOIRLab.
The host star, located in the constellation Aquila within the Milky Way, is slightly redder and dimmer than our sun, with roughly 70% of the sun's mass. The ill-fated planet is thought to have been a "hot Jupiter"—a massive gas giant with a tight, scorching orbit.
"We believe it probably had to be a giant planet, at least a few times the mass of Jupiter, to cause as dramatic of a disturbance to the star as what we are seeing," said Morgan MacLeod, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics and co-author of the study.
Webb's sensitive instruments revealed the aftermath: a ring of hot gas encircling the star and a growing cloud of cooler dust surrounding the scene—likely remnants of both the planet and expelled stellar material.
The team hypothesizes that over time, the planet’s orbit decayed due to gravitational interactions with the star. Eventually, it began skimming the stellar atmosphere, facing increasing drag and heat until it spiraled rapidly inward.
"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," said MacLeod.
"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," he added.
"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.
While none of the planets in our solar system are currently close enough to the sun for a similar fate, that may not be the case forever. In about five billion years, our sun is expected to enter its red giant phase, possibly engulfing Mercury, Venus, and even Earth before shedding its outer layers and becoming a white dwarf.
Still, these Webb observations suggest there may be more than one road to planetary demise.
"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," said Lau.