Jakob Walcher Research and Scientific Support Department, European Space Agency, Keplerlaan 1, 2200AG Noordwijk, The Netherlands Brent Groves Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands Tamás Budavári Dept. of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA Daniel Dale Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA