The only planet in our solar system that has a lower density than water and would therefore float is Saturn.

Here's why:

* Saturn's composition: Saturn is primarily composed of hydrogen and helium, which are very light elements.

* Low density: Saturn's average density is about 0.69 g/cm³, which is less than the density of water (1 g/cm³).

While it's tempting to imagine a giant planet floating in a giant bathtub, it's important to remember that this is a hypothetical scenario. There's no way to actually test this, and the immense pressure at the bottom of a hypothetical "bathtub" large enough to contain Saturn would likely crush any container.