Planets’ angled orbits attributed to the acquisition of Planet 9
In the beginning, there was dust, and it was flat. The bits of dust and rock swirling around our infant sun were spread out into a flat disk shape, congealing in various hunks that would eventually become planets like Earth and Saturn. Those planets would continue along the orbits of their originating dust, orbiting the Sun in along flat plane, at least until something happened that made the all the planets go just a bit wobbly.
The potential pull of Planet 9
That something may turn out to be the as-yet-undiscovered Planet 9, orbiting along the outer reaches of our solar system. The huge planet, expected to be at least five times the mass of Earth, isn’t thought to have come from the same orbiting dust as the rest of the planets. Instead, it may have been captured by our Sun’s gravitational pull later on, effectively being stolen from its native system. Since gravity is a two-way street, grabbing an extra planet likely exerted some influence on the original eight planets, and may have been disruptive enough to knock them off their original orientation around the Sun. If true, this would explain why the planets in our solar system don’t orbit in parallel to the Sun’s equator, but at a six-degree tilt.
This disruption wouldn’t be simply due to the mass of the new arrival, but to the tilt on Planet 9 when it was captured by our Sun’s gravity. A big object coming in from an angle would have provided the off-kilter pull necessary for our current orbits. This isn’t to say that raw mass doesn’t count, because Jupiter has altered orbits in its own right as well.
Jupiter’s odd orbit
Even if Planet 9 turns is found, and is huge, it’s probably going to be smaller than Jupiter. Jupiter is two-and-a-half-times bigger than all the known planets in the solar system combined, which means it’s big enough to exert a measurable pull on the Sun itself. Rather than orbit the center of the Sun directly, the balancing point between these two objects has actually settled out to be just outside the Sun’s perimeter. The Sun and Jupiter then orbit this empty, middle point, giving the Sun itself a bit of a wobble when compared to Jupiter. While the Sun is still the keystone of our solar system, it looks like the planets have been pushing back more than you’d expect.
Source: Planet Nine may have tilted entire solar system except the sun by Rebecca Boyle, New Scientist