Possible Signs of Water and Differentiation in a Rocky Exoplanetary Body
  Spitzer observations reveal the presence of warm debris from a tidally destroyed rocky and possibly icy planetary body orbiting the white dwarf GD 61. Ultraviolet and optical spectroscopy of the metal-contaminated stellar photosphere reveal traces of hydrogen, oxygen, magnesium, silicon, iron, and calcium. The nominal ratios of these elements indicate an excess of oxygen relative to that expected from rock-forming metal oxides, and thus it is possible that water was accreted together with the terrestrial-like debris. Iron is found to be deficient relative to magnesium and silicon, suggesting the material may have originated as the outer layers of a differentiated parent body, as is widely accepted for the Moon. 
J. Farihi, C. S. Brinkworth, B. T. Gaensicke, T. R. Marsh, J. Girven,   D. W. Hoard, B. Klein, D. Koester
astro-ph.EP astro-ph.SR