Star System With Right-Angled Planets Surprises Astronomers

Two planets orbit the poles while another revolves around the star’s equator, suggesting a mysterious, undetected 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 the 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 as Earth and the other planets in our system do.