Deuterium-enriched water binds planet-forming disks to comets and protostars


The observation of the water present in the disk that forms around the protostar V883 Ori has provided new clues about the formation processes of comets and planetesimals in our own Solar System.

A science team detected water in the circumstellar disk of a nearby protostar using the Atacama Large Millimeter/submillimeter Array (ALMA). It is the first time that water has been observed depositing in a protoplanetary disk without significant changes in its composition. This finding suggests that the water present in our Solar System formed billions of years before the Sun. The results of the study were published today in the journal Nature. V883 Orionis is a protostar located about 1,305 light years from Earth, in the constellation Orion. His observation allowed the scientific community to find a probable link between the water present in the interstellar medium and the water of our Solar System, by confirming that they have a similar composition.

“We can think of the path of water through the Universe as a path. We know the whereabouts, which are the planets and comets where there is water, but we wanted to trace their trace back to the origins of the water,” says John Tobin, an astronomer at the National Radio Astronomical Observatory (NRAO) of the National Science Foundation. of the United States (NSF) and lead author of the article. “Until now, we could link Earth to comets and protostars to the interstellar medium, but we couldn’t establish a link between protostars and comets. That changed with V883 Ori, and we now know that water molecules in that system and those in our Solar System have similar ratios of deuterium to hydrogen.” Observing water in the circumstellar disks of protostars is a complex task, since in most systems the water is frozen. When observing protostars, the scientific community looks for snow lines, or ice lines, where water transitions between ice and gas, which can be observed in greater detail using radio astronomy. “If the snow line is too close to the star, there isn’t enough gaseous water to detect it easily, and dust from the disk can mask a lot of the emissions from the water. If the snow line is far enough from the star, there may be detectable water vapor, and that is what has been observed in V883 Ori”, explains John Tobin, who adds that this research was only possible thanks to this feature. unique to the protostar.

V883 Ori’s disk is quite massive and just the right temperature to allow water to transition from a solid to a gas, making it ideal for studying the growth and evolution of solar systems at radio wavelengths. “This observation demonstrates the extraordinary ability of ALMA to study something so important to life on Earth: water,” celebrates Joe Pesce, NSF Program Officer for ALMA. “Elucidating processes important to life on Earth by observing them in more distant regions of the galaxy also helps us better understand how nature works in general and learn about the processes that allowed our Solar System to become what it is today.” To establish a relationship between the water in the protoplanetary disk of V883 Ori and the water in our Solar System, the research team studied its composition using ultrasensitive Band 5 (1.6 mm) and Band 6 (1.3 mm) receivers. and discovered that its composition remains relatively unchanged at each stage of solar system formation: from the protostar to the protoplanetary disk and comets. “This means that the water in our Solar System formed long before the Sun, planets and comets. We already knew that there is a lot of water in the interstellar medium. The results obtained now show that this water was directly incorporated into the Solar System during its formation,” says Merel van ‘t Hoff, an astronomer at the University of Michigan and co-author of the article. “This is very exciting, because it is an indication that other planetary systems must also have received large amounts of water.”

A good understanding of the role of water in the development of comets and planetesimals is essential to knowing exactly how our own Solar System formed. Although the Sun is believed to have formed in a dense cluster of stars, while V883 Ori lies relatively isolated in a starless zone, the two stars have one fundamental feature in common: they both formed in giant molecular clouds. “We know that most of the water in the interstellar medium is deposited as ice on the surface of tiny dust grains in clouds. When these clouds collapse under their own gravity and form new stars, the water is deposited in the surrounding disks. Over time, the disks evolve and the frozen dust grains clump together to form a solar system with planets and comets,” explains Margot Leemker, an astronomer at Leiden University and co-author of the article. “We have shown that the water that forms in clouds goes through these stages practically unchanged. So, by analyzing the water from the V883 Ori disk, we’re basically looking back in time and seeing what our own Solar System was like in its youth.

Resources “Deuterium-enriched water ties planet-forming disks to comets and protostars”, J. Tobin et al., 8 Mar 2023, Nature,