Sean wants to be the first to walk on a moon, like his hero Neil Armstrong. When Sydney points out that 12 astronauts have already walked on our Moon, Sean thinks that rather than be the 13th to walk on OUR moon, why not be the first to walk on ANOTHER moon in our solar system? Sure, but which moon? The kids decide to compare the frozen moons Europa, which orbits Jupiter, and Enceladus, which orbits Saturn. They get help from Carrot and Celery, who fly them to each one, and Sean gets to walk on them.