Where does Earth's water come from? (October 2011)

A just born star shooting water bullets! (June 2011)

Water is one of the most abundant and important molecules in star-forming regions. Although it is only a trace species in general molecular clouds, water becomes the third most abundant species in the warm regions created by the presence of newly-formed stars: the inner protostellar envelopes where the dust is warmer than the ice evaporation temperature, and the regions where the collapsing matter interacts with the powerful jets from the protostar causing violent shocks. This enormous variation in abundance makes water a unique probe of the physical structure of the region, and of the fundamental chemical processes within the gas and between the gas and the grains.

Moreover, its level of deuteration provides an important record of the temperature history of the cloud and the conditions during grain surface formation. Water also plays an active role in the energy balance of the envelope. In all of these physical and chemical aspects, water provides highly complementary information to that derived from the commonly studied CO molecule.

HIFI instrument

In this Herschel HIFI-led Key Program, we propose a comprehensive set of water observations towards a large sample of protostars, covering a wide range of masses and luminosities -from the lowest to the highest mass protostars-, and a large range of evolutionary stages -from the first stages represented by the pre-stellar cores to the last stages represented by the pre-main sequence stars surrounded only by their protostellar disks.

Lines of H₂O, H₂ ¹⁸O and the chemically related species O, OH, OH⁺ and H₃ O⁺ will be observed. In addition, selected high-frequency lines of CO and ¹³ CO as well as dust continuum maps will be obtained with Herschel, and will be complemented by ground-based HDO, CO and continuum maps to ensure a self-consistent data set for analysis. The HIFI instrument will be used for the bulk of the time, but PACS spectroscopy will be added as well. For more information, see out Outreach, Public images sites, or an overview presentation.