Liquid water that once flowed on the surface of Mars could now be locked up deep in the planet’s interior as an unusual form of ice, scientists reported earlier this month. In a paper published in the journal Nature December 14, Craig Bina of Northwestern University and Alexandra Navrotsky of the University of California at Davis said that water could be transported into the interiors of terrestrial planets, including the Earth and Mars, as “ice VII”, a rare, dense form of water ice that forms at high pressures and low temperatures.