Cosmic Mystery Stumps Astronomers: How Can Such a Huge Planet Orbit Such a Tiny Star?

Scientists are flummoxed about a planet recently discovered 51 light-years away in the Hercules constellation. By all rights, it shouldn’t exist, and it could force researchers to reconsider theories about how planets form. 

The planet orbits a small star, LHS 3154, around nine times smaller than the one at the center of Earth’s solar system. LHS 3154 is a so-called Class M star, and the planets that normally orbit Class M stars tend to be small and rocky like Earth and Mars. 

But the planet next to LHS 3154 is big — 13 times larger than Earth, much bigger than scientists expected. More confoundingly, it has a small orbit, revolving around its star every 3.7 days. Based on past scientific thought, it should be impossible for a planet that large to exist so close to a sun that small, according to the research published in Science on Thursday by a team of international astronomers. 

For now, the scientists have no explanation for how this planet and star paired up, and when they use computer simulations to examine their relationship, they found that such a planet would need 10 times the amount of space dust — a basic building block for planets — than normally found near M Class stars.  

In their paper, the researchers suggested that scientists may need to rethink what they thought they knew about how planets form. While it was previously believed that the creation of planet might take several million years, the team wrote that their discovery could mean the process is relatively speedy: less than a million years after the birth of their host star.