Final answer:
Saturn and Jupiter lack a clear division between their atmospheres and surfaces due to being gas giants with deep atmospheres composed mainly of hydrogen and helium, which become denser and transition into a liquid state without a solid boundary.
Step-by-step explanation:
The reason there is no clear division between the atmosphere and the surface on planets like Saturn and Jupiter is because they are gas giants composed predominantly of hydrogen and helium. These elements are gases under the conditions found on Earth but are highly compressed within these large planets, with the sheer pressure turning hydrogen into a liquid in their deeper layers. Consequently, Saturn and Jupiter have deep atmospheres and lack a solid surface, which means as one descends through their atmospheres, gases gradually become denser until they liquify, creating a seamless transition from the atmosphere to the 'surface,' which is actually a transition into a denser fluid state.
Jupiter is known to be 318 times more massive than Earth and possesses an extensive mantle of liquid hydrogen similar to Saturn. Both planets have high-speed winds and prominent storms in their atmospheres, leading to a dynamic and ever-changing cloud system. These deep atmospheres are also responsible for obscuring any solid core that may exist deeper within these planets, adding to the lack of a defined surface compareable to terrestrial planets.