Star system with right-angled planets surprises astronomers

Two planets orbit the poles while another revolves around the star's equator, suggesting a mysterious force

Star systems come in all shapes and sizes. Some have lots of planets, some have larger planets and others have no planets at all. But a particularly unusual system about 150 light-years from our own has scientists scratching their heads.

In 2016, astronomers discovered two planets orbiting the star HD 3167. They were thought to be super-Earths — between Earth and Neptune in size — and circled the star every one and 30 days. A third planet was found in the system in 2017, orbiting in about eight days. What’s unusual is the inclinations of the outer two planets, HD 3167 c and d. Whereas in our solar system all planets orbit in the same flat plane around the sun, these two are in polar orbits. That is, they go above and below their star’s poles, rather than around the equator.

Now scientists have discovered the system is even weirder. Researchers measured the orbit of the innermost planet, HD 3167 b, for the first time — and it doesn’t match the other two. It instead orbits in the star’s flat plane, like planets in our solar system, and perpendicular to HD 3167 c and d. This star system is the first one known to act like this. “It was clearly a surprise,” said Vincent Bourrier, from the University of Geneva in Switzerland, who led the discovery published last month in the journal Astronomy & Astrophysics. “This is something radically different from our own solar system.” Were you to stand on one you would see a rather intriguing view. “If you had a telescope and you were looking at the trajectory of the other planets in the system, they would be going vertically in the sky.”

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