Following the water throughout star formation via its deuteration ratio in ices

The question of how water forms and evolves throughout star and planet formation is not only crucial for understanding how life was able to evolve on Earth, but also whether life can evolve in other solar systems. Due to the sensitivity of deuteration processes to physicochemical conditions, the deuterium abundance of water provides a window into the environment in which it formed and existed. Recent JWST data show that the unprecedented sensitivity of the NIRSpec IFU at 4.1 um enables robust measurement of the HDO/H2O ratio of interstellar ices for the first time, providing a clear path to characterizing the link between prestellar water ice and the water found in solar system bodies such as our Earth, comets, moons, and water-rich asteroids.

We propose to search for HDO ice with NIRSpec IFU in three prestellar cores and three low-mass protostars. In these objects, we will constrain the column densities and morphologies of H2O ice via the O-H stretching band at 3 um and HDO ice via the O-D stretching band at 4.1 um, which can only be observed via G395M when observing with NIRSpec IFU. We will also constrain the CH3OH ice column density via the 3.53 um band to ensure that any observed absorptions at 4.1 um cannot be attributed instead to CH3OH. The use of the IFU will enable correlation of ice morphologies in extended sources. In two of the low-mass protostars, the ratios in measured in the ices will be compared to their gas-phase HDO/H2O ratios obtained by ALMA. The proposed observations will probe more deeply than before the physicochemical history of water and evaluate if prestellar water ice is inherited by protoplanetary disks and bodies that form within them.