https://www.scientificamerican.com/article/did-a-stellar-intruder-deform-our-outer-solar-system/

There is a mystery brewing in the far reaches of our solar system.

Astronomers have long thought the eight planets orbit in nearly perfect circles because they once formed within the swirling disk of dust and gas that surrounded the young sun. But in 2003 scientists discovered something strange: a dwarf planet known as Sedna whose elongated orbit takes it from twice Pluto’s distance to more than 20 times its distance from the sun. And it is not alone. In the years since astronomers have uncovered nearly two dozen distant icy objects whose orbits are oblong and strangely tilted compared to the plane of the solar system. To explain such oddities, scientists speculated that maybe these worlds are scars from a violent past, a sign something—perhaps a passing star—knocked them off course in our solar system’s infancy. Or maybe there is a distant ninth planet whose gravity sculpts their peculiar orbits.