We present techniques to index mobile objects in order to efficiently answer range queries about their future positions. This problem appears in real-life applications, such as predicting future congestion areas in a highway system, or allocating more bandwidth for cells where high concentration of mobile phones is impending. We address the problem in external memory and present dynamic solutions, both for the one-dimensional, as well as the two-dimensional cases. Our approach transforms the problem into a dual space that is easier to index. Finally we discuss advantages and disadvantages among the various schemes proposed in literature for indexing mobile objects.