Star likely gobbled its own planets, astronomers say

About 320 light-years from Earth is a sun-like star astronomers suggest likely consumed its planets.

Unusual composition of star suggests it swallowed planets that came too close

Binary stars, similar to these depicted here by an artist's rendering, share a point of orbit. It's believed that one of those stars, HD 240430, has consumed several planets. (Casey Reed/NASA)

It was a star with a hefty appetite.

Astronomers say the sun-like star about 320 light-years from Earth may have eaten several of its planets, leading them to give it the nickname Kronos, after the Greek god who ate his sons.

The star — with the official name of HD 240430 — is believed to be part of a wide binary star system, two stars that share a central point of orbit. Because the stars travel together in space, astronomers refer to them as co-moving stars.

While the stars are believed to have formed together about four billion years ago, astronomers studying their compositions discovered that they were quite different from one another.

The second star in the system, HD 240429 (with the nickname of Krios after the brother of Kronos), had lower levels of elements like lithium, iron and magnesium. This wouldn't make sense if the stars had formed as a pair.

"I absolutely thought I was doing something wrong," lead author of the study, Semyeong Oh, told CBC News. "When I found out they had such different abundancies … I thought it couldn't possibly be explained."

The only explanation for the abundance of elements not present in Krios would be if Kronos had consumed a rocky planet rich with those particular elements, researchers concluded. 

Other stars have high levels of such elements, but not in such abundance.

In this artist's concept, the atmosphere of exoplanet WASP-12b is seen flowing into its parent star. It's known that some gaseous planets close to their parent star can lose their atmosphere in this manner. (Artwork Credit: NASA, ESA, and G)

"It's the first time we saw this in such magnitude," said Oh.

For the elements like iron and magnesium, there was roughly a 60 per cent difference between the two stars. Comparatively, Oh said, other findings of binary stars have been around a 10 per cent difference. 

Planetary formation

After the birth of a star, there is a disk of leftover material that orbits it. This is the material that coalesces to form planets.

How a star might have consumed its planets isn't understood, since they should have remained in a somewhat stable orbit.

One way a planet — or planets — could have destabilized, the researchers say, is from the gravity of a passing star. This could have changed the orbits of the outer planets and affected the orbits of the planets nearest the star.

They're giving us quite a picture of the remarkable diversity of planets and planetary systems.- Ray Jayawardhana, dean of science, York University

As for how the planet or planets may have met their demise, it's likely they would have been eaten whole rather than breaking apart before being consumed.

"It would probably pull it into the surface of the star and then it would disrupt in there," Adrian Price-Whelan, co-author of the paper, told CBC News. 

Ray Jayawardhana, dean of science and a professor of physics and astronomy at York University in Toronto, said the findings were intriguing.

"In a sense they're doing archeology of planetary systems," he said. "You're looking at possible remnants of planetary or protoplanetary [pre-planetary] bodies that are no more." 

The findings are important to planetary scientists and those who study stars, as it helps them gain a better understanding of the different stars and their planetary companions.

"They're giving us quite a picture of the remarkable diversity of planets and planetary systems," Jayawardhana said.


Nicole Mortillaro

Senior Reporter, Science

Nicole has an avid interest in all things science. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books.