To have a ninth planet (no, not again… Pluto is no more a full-sized planet since a while) might be not enough, and here we were already happy… Now it might be possible that such a ninth/never seen/hypothetical planet has also extrasolar origin.
Since the announcement of a possible further planet well hidden in the deep dark and cold outskirts of our solar system evidences for Planet Nine’s existence has continued to mount.
The very last clue is that the planet might be the true reason why the orbits of the other planets, something that we know rather well since hundreds of years, are crooked (OK, Mercury is slightly different, but that’s another story).
Orbits of all the planets, indeed, are slightly askew. All of them revolve roughly in the same plane, but this plane is not the plan where the Sun rotates in. There are about 6 degree difference that can not be explained “easily” due to the conservation of momentum. Basically since the largest part of the mass of our solar system is contained into the Sun… it rules. And if it revolves in a given plane it is expected that everything else revolves in the same plane.
Nonetheless we have 6 degrees of separations (that looks like a “Bart S. rule”).
“The inclination of the planetary system relative to the solar equator may be explained by the presence of Planet 9” is a paper presenting this scenario. The effects of the presence of a massive highly inclined body is investigated and in particular is is studied how the orbits of the other planets might be affected. It results that the precession of the planets’ orbital planes can be explained with the presence of an inclined planet giving results compatible with the actual orbital positions. Indirect and fascinating clue!
Such a difference has been so far explained by calling for an external object that entered/passed close to our solar system during the early years of formation messed with all the orbits. But Planet Nine can explain these 6 deg as well. Indeed it can explain the difference much better than a casual and fast passage of a star in the ancient solar system. Since its orbit is (hypothesized) to be highly inclined, its gravity pull might have been the dragged all the other planets off-axis during the solar system’s early days.
“Some of the planet 9 configurations that allow explaining the current solar tilt are compatible with those proposed to explain the orbital confinement of the most distant Kuiper belt objects.”
But wait. If this is correct, how is it possible that Planet Nine has such inclined orbit? Well, if it is an exoplanet captured during solar system formation. Of course.
We haven’t’ seen the plant yet, but if it is there we have at least a clue where to search for it.