As the pace of discovery quickened and new data came pouring in, it became clear that the cosmos is awash in planets—big planets, small planets, planets broiled by their stars or frozen in the outskirts of their systems and, overwhelmingly, planets that in size and orbit are unlike anything we have in the solar system. Unlike what a diver finds, however, pressures inside planets are so high that matter itself takes on baffling new forms. “At those pressures, matter behaves in ways we don’t really understand.”That’s where the giant lasers and gargantuan electromagnets come in. The usual way planetary scientists push matter to high pressures is to squeeze tiny samples of rock or metal between two diamonds. That is, planetary scientists have several sound theoretical ideas about how matter might behave at really high pressures, but they have lacked data.