* The sun is a sphere, and planets are not perfectly shaped for packing. You can't just stack planets like oranges.
* Planets vary in size. Jupiter is much larger than Mercury.
* The question doesn't define how we're "fitting" them. Do we try to pack them tightly? Do we allow them to overlap?
However, we can get a rough idea:
* The sun's volume is about 1.3 million times larger than Earth's.
* The combined volume of all planets in our solar system is less than 1/1000th the sun's volume.
This means you could theoretically fit a *lot* of Earths inside the sun. But even with all the planets in our solar system combined, they would only occupy a tiny fraction of the sun's space.
