In a paper published Dec. 14 in the journal Nature, Northwestern University geologist Craig R. Bina reports that, in a novel twist on current thinking, water may be transported into the interior of planets as a high-pressure form of ice, rather than simply being transported while trapped within hydrous minerals or escaping as a fluid. Bina and co-author Alexandra Navrotsky, a chemist and materials scientist from the University of California, Davis, suggest that this process should become more important as planets cool, for example on a future Earth or on Mars.