Facchini, StefanoTesti, LeonardoHumphreys, ElizabethVander Donckt, MathieuIsella, AndreaWrzosek, RamonBaudry, AlainGray, Malcom D.Richards, Anita M. S.Vlemmmings, Wouter2024-10-082024-10-082024Facchini, S., Testi, L., Humphreys, E., Vander Donckt, M., Isella, A., Wrzosek, R., Baudry, A., Gray, M. D., Richards, A. M. S., & Vlemmings, W. (2024). Resolved ALMA observations of water in the inner astronomical units of the HL Tau disk. Nature Astronomy, 8(5), 587–595. https://doi.org/10.1038/s41550-024-02207-whttps://hdl.handle.net/1911/117941The water molecule is a key ingredient in the formation of planetary systems, with the water snowline being a favourable location for the growth of massive planetary cores. Here we present Atacama Large Millimeter/submillimeter Array data of the ringed protoplanetary disk orbiting the young star HL Tauri that show centrally peaked, bright emission arising from three distinct transitions of the main water isotopologue ($${\mathrm{H}}_{2}^{16}{\mathrm{O}}$$). The spatially and spectrally resolved water content probes gas in a thermal range down to the water sublimation temperature. Our analysis implies a stringent lower limit of 3.7 Earth oceans of water vapour available within the inner 17 astronomical units of the system. We show that our observations are limited to probing the water content in the atmosphere of the disk, due to the high dust column density and absorption, and indicate that the main water isotopologue is the best tracer to spatially resolve water vapour in protoplanetary disks.engExcept where otherwise noted, this work is licensed under a Creative Commons Attribution (CC BY) license. Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Journal articles41550-024-02207-whttps://doi.org/10.1038/s41550-024-02207-w