Possibility to locate the position of the H₂O snowline in protoplanetary disks through spectroscopic observations

Observationally locating the position of the H₂O snowline in protoplanetary disks is crucial for understanding planetesimal and planet formation processes, and the origin of water on the Earth. In our studies, we conducted calculations of chemical reactions and water line profiles in protoplanetary disks, and identified that ortho/para-H₂¹⁶O, H₂¹⁸O lines with small Einstein A coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the H₂O snowline. Therefore, through analyzing their line profiles the position of the H₂O snowline can be located. Moreover, because the number density of the H₂¹⁸O is much smaller than that of H₂¹⁶O, the H₂¹⁸O lines can trace deeper into the disk and thus they are potentially better probes of the exact position of the H₂O snowline in disk midplane.