  Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um
spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice
absorption bands superposed on steeply rising mid-infrared continua. The ices
likely originate in the circumstellar envelopes. The CO2 bending mode at 15 um
is a particularly powerful tracer of the ice composition and processing
history. Toward these protostars, this band shows little evidence for thermal
processing at temperatures above 50 K. Signatures of lower temperature
processing are present in the CO and OCN- bands, however. The observed CO2
profile indicates an intimate mixture with H2O, but not necessarily with CH3OH,
in contrast to some high mass protostars. This is consistent with the low CH3OH
abundance derived from the ground based L band spectra. The CO2/H2O column
density ratios are high in both B5 IRS1 and HH46 IRS (~35%). Clearly, the SST
spectra are essential to study ice evolution in low mass protostellar
environments, and to eventually determine the relation between interstellar and
solar system ices.
