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'Planetary Heist': These Star Systems Might Contain Stolen Planets

A new study has unveiled evidence of cosmic crime. Here are the facts.

Monisha Ravisetti Former Science Writer
Monisha Ravisetti was a science writer at CNET. She covered climate change, space rockets, mathematical puzzles, dinosaur bones, black holes, supernovas, and sometimes, the drama of philosophical thought experiments. Previously, she was a science reporter with a startup publication called The Academic Times, and before that, was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. When she's not at her desk, she's trying (and failing) to raise her online chess rating. Her favorite movies are Dunkirk and Marcel the Shell with Shoes On.
Monisha Ravisetti
3 min read
An illustration in dark, sort of ominous, tones that showcase a small, bright star in the background in space. In the foreground is a large planet that seems to have rings like Saturn.

Jupiter-like planets aren't supposed to be around some stars. So why are they there? Or rather, where did they come from?

University of Sheffield

In astronomy, a rule of thumb states that if a star is over three times as massive as our sun, it probably can't have planets as big as Jupiter. 

The reasoning feels pretty intuitive. Huge stars emit huge amounts of radiation, therefore creating an environment far too toxic for budding worlds to reach the size of our solar system's gas giant -- a sphere so colossal it could fit about 1,300 Earths inside. "Whilst planets can form around massive stars, it is hard to envisage gas giant planets like Jupiter and Saturn being able to form in such hostile environments, where radiation from the stars can evaporate the planets before they fully form," Richard Parker, an astrophysicist at the University of Sheffield, said in a statement.

Yet (as usual) some cosmic realms seem to defy science as we know it. 

In recent years, scientists have identified at least two bizarre planetary systems with both a Jupiter-size planet and a very, very large star. Coincidence? Anomaly? Erroneous discovery? Perhaps not. On Wednesday, Parker and fellow researchers from the University of Sheffield in England offered up their working theory to solve the mystery -- and, well, it's not easy to say.

Maybe some massive stars are thieves, they suggest. 

Maybe some stole Jupiter-size worlds from smaller star peers to carry around as if it were their own.

"Essentially, this is a planetary heist," said Emma Daffern-Powell, an astronomer at the University of Sheffield and co-author of a study on the theory, published Wednesday in Monthly Notices of the Royal Astronomical Society.

Sneaky star high jinks

Though our universe is a melting pot of stars, even the most contradictory stellar bodies could've been birthed from the same embers of gas and dust. 

Stars share stellar nurseries.

This is, according to the team's new study, the root of the robbery at hand. 

Because planets tend to arise in those stellar nurseries too, either right by their corresponding host star or free-floating in outer space, they can be stolen by a neighboring star. Especially if that star is a lot stronger than the true parent star. "We know that massive stars have more influence in these nurseries than sun-like stars, and we found that these massive stars can capture or steal planets -- which we call 'BEASTies,'" Daffern-Powell said.

A sliver of the sun is seen on the left side of this image, and all of our solar system's planets are laid out from left to right. Jupiter looks absolutely gigantic compared to the Earth.

Check out the size different between Earth (third planet from the sun on the left) and Jupiter (fifth planet from the sun on the left).

NASA/Lunar and Planetary Institute

"The BEAST planets are a new addition to the myriad of exoplanetary systems, which display incredible diversity, from planetary systems around sun-like stars that are very different to our solar system, to planets orbiting evolved or dead stars," Parker said.

In short, the research team reached this conclusion by using computer simulations to show that the clever BEASTies could very well be captured or downright abducted, on average, once in the first 10 million years of a star-forming region's evolution.

The comforting news is that we may have our solar system's beloved Jupiter because, long ago, the sun wasn't massive enough to thwart the planet's growth goals. But, on the other hand, it's quite unsettling to know that, as Parker puts it, "our results lend further credence to the idea that planets on more distant orbits -- more than 100 times the distance from Earth to sun -- may not be orbiting their parent star."