Interstellar Comet Carries Water Unlike Anything in Our Solar System
Ben Sullivan
At the centre of a water molecule, tucked inside its hydrogen atom, there is usually just a single proton. Nothing else. But in a small fraction of the water on Earth, and in comets and asteroids scattered throughout our solar system, that proton has a neutron companion, making the hydrogen heavier, turning H2O into something denser and slightly more sluggish: deuterated water, or HDO. The ratio of this heavy water to ordinary water encodes, in a way, the entire thermal history of wherever it...