TITAN Titan is Saturn’s biggest moon. In some ways, it looks familiar, but not quite. Rocks on its surface are made of ice. T ick orange clouds fill the sky. Liquid methane fills the rivers and lakes. On Earth, methane is a gas. Dunes cover Titan. T ey look like


the sand dunes on Earth. Here’s a surprise! Titan’s dunes aren’t made of sand. T ey’re made of chemical bits. T ese bits fall from the orange clouds. T en whipping winds slowly sweep them into dunes. Titan has enough dunes to cover all of Australia.


Our Solar System Geologists study the solar system by making comparisons. We compare the planets and moons to Earth. T at can tell us a lot. For example, it can tell us how quickly or slowly features on other worlds change. Sometimes, we find things that are


new. T ese discoveries may make us rethink what we thought we knew. In this way, we can learn a lot about both Earth and distant worlds. We have learned that these worlds


all have something in common. Just like on Earth, some changes in space happen quickly, others more slowly.


This illustration shows how the winds on Titan have built giant dunes over time.


The winds on Earth slowly piled sand up into this dune.


erosion: a process in which rock is moved from one place to another by water, wind, or ice


geology: the science that deals with Earth’s physical structure, its history, and the processes that act on it


sediment: the particles of soil or rock that have been moved and deposited by water, wind, or ice


weathering: a process in which rocks are broken into smaller pieces


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