Spitzer Spectroscopy of Ices: From Molecular Cores to Planet-Forming Disks

Icy grain mantles are a major reservoir of the molecular inventory of dense clouds and circumstellar envelopes and disks. The ice abundances and in particular the dependence of abundances on the astrophysical environment are still poorly characterized. Numerous physical and chemical processes may modify the ices in the evolutionary sequence from dense cores to planet-forming disks. Using Spitzer/IRS and ground-based thermal infrared spectrometers we determine the ice inventory toward low mass protostars and address questions on evolutionary scenarios. The initial results from our Spitzer Legacy program “From Molecular Cores to Planet-Forming Disks” (c2d) indicate that ice abundances relative to H_2O commonly vary by factors of 2–5 in different sight-lines. For some species (CO) outgassing is likely responsible, but for others (CH_3OH, CO_2, NH_3) different factors, such as cloud history, must be involved