Scientists don't believe comets come from specific planets. Instead, they believe comets originate from two main regions within our solar system:

1. The Kuiper Belt: This is a disk-shaped region beyond Neptune, containing icy objects and dwarf planets like Pluto. Many short-period comets, those with orbital periods of less than 200 years, are thought to originate from this region.

2. The Oort Cloud: This is a theoretical spherical cloud surrounding the solar system, much further out than the Kuiper Belt. It is thought to be the source of long-period comets, with orbital periods of thousands of years.

So, while comets are not from specific planets, they originate from these two regions far beyond the orbits of the planets.