Is our world ordinary or special? It's hard to say yet.
An international team of researchers, mainly astronomers from the University of Geneva in Switzerland, recently published an article in astronomy and astrophysics that in the direction of Pisces, in a peculiar planetary system, the three known planets orbit not in one plane, but at an angle of nearly 90 degrees. The reason for such a chaotic layout may have something to do with the fact that the star has an unknown companion star.
The host star of this planetary system, named HD3167, is about 149 light-years from Earth and is known to host three planets. Its nearest planet, HD3167b, is a "super-Earth" with an orbital period of only 23 hours. The planet's orbital plane and HD3167's equatorial plane are parallel. But the orbital planes of the other two planets, HD3167c and HD3167d, are almost perpendicular to the equatorial plane of HD3167, meaning that they pass over the north and south poles of HD3167 once every revolution. HD3167c and HD3167d are both so-called "mini-Neptunes" with orbital periods of 8.5 and 29.8 Earth-days, respectively.
This orbital layout is very different from the solar system we live in. All the large planets in the solar system orbit in a plane that is parallel to the sun's equatorial plane.
This layout is related to the characteristics of the formation process of planetary systems. Planetary systems are usually formed sequentially with the birth of stars. A cloud of gas that nurtures a star usually has angular momentum, meaning that it naturally rotates and causes the star to rotate, and forms a giant disk of disk of material centered on the star near a plane perpendicular to the star's axis of rotation— that is, a plane parallel to the equatorial plane.
It is from this disk of material that planets are further formed. This disk of matter rotates around the star. This means that all protoplanets will also orbit the star in the same direction in the same plane. That's how our solar system is, and we've become accustomed to that layout.
But now it seems that not all planetary systems have this layout. The reason why HD3167 has such a strange planetary layout may be related to the existence of a companion star around HD3167 that has not yet been discovered. Under the influence of the gravitational pull of this companion star, the orbits of the two planets farther away from HD3167 have undergone a huge deflection; and HD3167b is still decisively dominated by the gravitational pull of HD3167 because of its proximity to the host star, and can still operate on a plane parallel to the equatorial plane of HD3167.
We are indoctrinated from an early age with the idea that our earth is ordinary, our sun is ordinary, and our solar system is ordinary. To some extent this is true. But in fact, most stars in the universe have at least one companion star, and a single star like our sun is relatively rare. So this alien world, which seems very strange to us, may help us think about some seemingly simple questions, how ordinary is our earth, our sun, our solar system? And what is ordinary?
reference
The Rossiter-McLaughlin effect Revolutions: an ultra-short period planet and a warm mini-Neptune on perpendicular orbits
http://dx.doi.org/10.1051/0004-6361/202141527