There have been a lot of discussions lately about the potential existence of a “Planet Nine” in the far reaches of our solar system. We used to think of this potential planet as a tenth planet, but that was before the classification of Pluto was changed. If it exists, Planet Nine could have any number of features. But if it is a large, rocky planet, it might substantially change the fate of our solar system.
In about seven billion years, our sun is going to start to die. When that happens, it will expand and engulf the first three planets (which includes Earth, of course) and push the gas giants out to a safe distance.
If there is a large, rocky Planet Nine though, that might actually get pulled closer by the process, which will interfere with the orbits of Uranus and Neptune, most likely resulting in their being ejected from the solar system. It’s a possibility that Planet Nine might also break apart during this process, resulting in rock debris orbiting the Sun, which by that point would become a white dwarf star.
Of course, none of this is likely to affect us very much, since the Earth will be destroyed no matter what. But, it might give us a clue as to why a significant number of white dwarf systems have such rocky debris in them, and tell us a little more about how those stars are formed.
If this is the case, then maybe we can learn more about the life cycle of white dwarf stars, and therefore more about our universe. We’ve discovered lately that there are far more Earth-like planets out there than we had previously expected. If such rocky planets exist in larger forms further from their stars, and thus are able to become debris after a star becomes a white dwarf, that challenges even more assumptions we’ve had about the universe.