The formation of water in the atmosphere of the dying star CW Leonis has puzzled astrochemists since its discovery in 2001. Now, data from the Herschel infrared space observatory suggest that the carbon star is surrounded by a gigantic cloud of hot water vapor because of ultraviolet-initiated photochemistry . Data from spectrometers, the SPIRE and Photoconductor Array Camera, and Spectrometer (PACS) instruments on board Herschel reveal stellar chemistry and temperature and suggest that UV breaks down carbon monoxide releasing oxygen to react with hydrogen forming the incredibly hot water.

• Warm water vapor in the sooty outflow from a luminous carbon star
  L. Decin, M. Agúndez, M. J. Barlow, F. Daniel, J. Cernicharo et al.,
  Nature, 2010, 467, 64-67.
  DOI: 10.1038/nature09344