R. Ibata, G. Lewis, A. Conn, M. Irwin, A. McConnachie, S. Chapman, M. Collins, M. Fardal, A. Ferguson, N. Ibata and 6 other author(s). (2013)cite arxiv:1301.0446Comment: Published in the 3rd Jan 2013 issue of Nature. 19 pages, 4 figures, 1 three-dimensional interactive figure. To view and manipulate the 3-D figure, an Adobe Reader browser plug-in is required; alternatively save to disk and view with Adobe Reader.