Water in the Stars...

...or at least found on the former planets around them.

Most stars (including, in about 4 billion years, our sun) end their lives as white dwarfs, after they have burned all their nuclear fuel. These super dense stellar embers exert such strong gravity that any element heavier than helium will immediately sink to the dwarf’s core. So imagine astronomers’ surprise when they discovered that some white dwarfs are cloaked in layers of “pollution” made up of silicon, oxygen, and other elements much higher up on the periodic table.

This pollution is made up of “pieces of planetary systems that are falling into their central stars,” explains Jay Farihi, an astronomer at the University of Cambridge in the United Kingdom. By measuring the pollution’s constituent elements, scientists can peer back in time and discover what the original solar system’s asteroids, comets, and planets were made of. “It’s a wonderful technique for doing planetary forensics,” says Michael Jura, a white dwarf expert at the University of California, Los Angeles, who wasn’t involved in the current research.

In GD 61’s pollution, Farihi and his colleagues noticed a curious abundance of oxygen. Their first thought was that the original asteroid must have been encrusted with carbon dioxide in the form of dry ice. Trouble is, there was no carbon anywhere to be found around GD 61. So in order to account for the extra oxygen, “the only chemically viable substance left is water,” Farihi says.

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