Just they did with Pluto they can “see” the evidence to a pretty big mass somewhere out there because of the gravity it exerts.
It will be interesting to see how this develops. If it has an orbit different than all of the other planets it could cause some disruption and it comes in towards the sun.
I hope it’s a few hundred years from now.
Our solar system is not in the central disk of the Milky Way, but swings back and forth across the dense central disk roughly every 30 million years. I have been looking to see if there is correlation with galactic plane crossings and mass extinctions. So far no luck, but 30 million years and 26 million years may be measurement error, but is far too long for the orbit of a planet. There could be a 9th planet and they are looking with much better equipment. I am just not convinced there is enough evidence to say more than it could be.