Recipe for water: just add starlight ESA’s Herschel infrared
space observatory has discovered that ultraviolet starlight is
the key ingredient for making water in space. It is the only
explanation for why a dying star is surrounded by a gigantic
cloud of hot water vapour. Every recipe needs a secret
ingredient. When astronomers discovered an unexpected cloud of
water vapour around the old star IRC+10216 in 2001, they
immediately began searching for the source. Stars like IRC+10216
are known as carbon stars and are thought not to make much
water. Initially they suspected the star’s heat must be
evaporating comets or even dwarf planets to produce the water.
Now, Herschel’s PACS and SPIRE instruments have revealed that
the secret ingredient is ultraviolet light, because the water is
too hot to have come from the destruction of icy celestial
bodies. “This is a good example of how better instruments can
change our picture completely,” says Leen Decin, Katholieke
Universiteit Leuven, Belgium, the lead author of the