On alien planets, they rain from the sky as scalding iron. On distant moons, even at hundreds of degrees below zero, they slosh around in pristine lakes of methane. They can cover entire planets in miles-deep oceans of electrified hydrogen metal. Or erupt on alien worlds through miles-high geysers. They churn in the interiors of dead stars and even our own planet. They're so rare in the universe, they almost don't exist, but these are the magical liquids of our Liquid Universe.

• Neil deGrasse Tyson
• Erik Thompson
• Alex Filippenko

• David Brin
• David Ackroyd
• Michio Kaku