By observing the changing patterns in sand dunes, scientists can learn about the interaction between the Martian surface and the atmosphere. Dune activity can help us understand that rate at which the Martian wind moves sediments around, as well as to estimate how long it takes for windblown sand to abrade the surfaces of rocks; not to mention our Mars landers. Dunes were first detected by the Mariner 9 spacecraft in the early 1970s, and are actively studied by the Mars Global Surveyor orbiter today.