Water is an essential ingredient for the emergence of life as we know it. On Earth, most of the water in our oceans was formed long before the birth of the Solar System, in the cold regions of interstellar space (-250°C). However, a fraction of this water could have been destroyed and re-formed at higher temperatures (100-500°C) when the Solar System was still just a disk of gas and dust orbiting our nascent Sun.
To understand this enigmatic recycling of water, astronomers pointed the JWST towards "d203-506", a planet-forming disk located in the Orion Nebula, a planetary system nursery. The intense ultraviolet radiation produced by nearby massive stars leads to the rapid destruction and reformation of water in d203-506, making it a true interstellar laboratory.
But how can the formation and destruction of molecules located more than 1,000 light-years away be observed? A collaboration with quantum dynamics experts , was the key to meeting this challenge. When water (H2O) is destroyed by ultraviolet light, a hydroxyl radical (OH) is released with a fast spinning (rotational) state. This is followed by the emission of photons which travel to and are detected by the JWST. In total, it is estimated that the equivalent of a terrestrial ocean is destroyed every month in the young system d203-506.
However, it doesn’t end there. Via a similar mechanism of near-infrared photon emission, JWST reveals that hydroxyl is produced in abundance from atomic oxygen by the O+H2 reaction. Hydroxyl is a key intermediate in the formation of water, as it then reacts with H2 to form water via the OH+H2 reaction. The destruction/formation cycle is complete. Some of the water making up our oceans could indeed have undergone such a cycle.
![<multi>[fr]A gauche et au centre : le jeune disque d203-506 enfoui dans la Nébuleuse d'Orion vu par le JWST A droite : Animation/Schéma illustrant comment la formation et destruction de l'eau a pu être révélée par les observations JWST. [en]Left and center: the young d203-506 disk buried in the Orion Nebula as seen by JWST. Right: Animation/Schematic illustrating how the formation and destruction of water was revealed by JWST observations.</multi>](IMG/png/capture_d_e_cran_2024-02-22_a_16.12_46.png)
Mais l’histoire ne s’arrête pas là. Par un mécanisme similaire d’émission de photons dans l’infrarouge proche, JWST nous révèle que l’hydroxyle est produit en abondance à partir de l’oxygène atomique par la réaction O+H2. Or celui-ci est justement un intermédiaire clé dans la formation de l’eau puisqu’il réagit ensuite avec H2 pour former l’eau par la réaction OH+H2. Le cycle de destruction / formation est bouclé. Une partie de l’eau constituant nos océans pourrait être passée par un tel cycle.
Reference
OH as a probe of the warm water cycle in planet-forming disks
Marion Zannese, Benoît Tabone, Emilie Habart, Javier R. Goicoechea, Alexandre Zanchet, Ewine F. van Dishoeck, Marc C. van Hemert, John H. Black, Alexander G. G. M. Tielens, A. Veselinova, P. G. Jambrina, M. Menendez, E. Verdasco, F. J. Aoiz, L. Gonzalez-Sanchez, Boris Trahin, Emmanuel Dartois, Olivier Berné, Els Peeters, Jinhua He, Ameek Sidhu, Ryan Chown, Ilane Schroetter, Dries Van De Putte, Amélie Canin, Felipe Alarcón, Alain Abergel, Edwin A. Bergin, Jeronimo Bernard-Salas, Christiaan Boersma, Emeric Bron, Jan Cami, Daniel Dicken, Meriem Elyajouri, Asunción Fuente, Karl D. Gordon, Lina Issa, Christine Joblin, Olga Kannavou, Baria Khan, Ozan Lacinbala, David Languignon, Romane Le Gal, Alexandros Maragkoudakis, Raphael Meshaka, Yoko Okada, Takashi Onaka, Sofia Pasquini, Marc W. Pound, Massimo Robberto, Markus Röllig, Bethany Schefter, Thiébaut Schirmer, Sílvia Vicente, Mark G. Wolfire
Nature Astronomy 23 February 2024 https://arxiv.org/abs/2312.14056