V883 Ori is a remarkable protostar that boasts a temperature just hot enough to turn water in its circumstellar disk into gas. This gas can be studied by radio astronomers to trace the origin of water. Recently, ALMA observations have confirmed that the water in our own solar system may have the same source as the water found in disks surrounding protostars in other parts of the universe – the interstellar medium. Credit: ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)
ALMA traces the history of water in planet formation back to the interstellar medium
Observations of water in the disk forming around the protostar V883 Ori have revealed clues about the formation of comets and planetesimals in our own solar system.
Scientists studying a nearby protostar have discovered the presence of water in its circumstellar disk. The new observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) mark the first detection of water being inherited into a protoplanetary disk without significant changes in its composition. These results further suggest that the water in our solar system formed billions of years before the Sun. The new observations were published on March 8 in the journal Nature.
This artist’s impression shows the planet-forming disk around the star V883 Orionis. In the outermost part of the disc, the water freezes out as ice and therefore cannot be easily detected. A burst of energy from the star heats the inner disk to a temperature where water is gaseous, allowing astronomers to detect it.
The inset image shows the two kinds of water molecules studied in this disc: normal water, with one oxygen atom and two hydrogen atoms, and a heavier version where one hydrogen atom is replaced with deuterium, a heavy isotope of hydrogen.
Credit: ESO/L. way
V883 Orionis is a protostar located about 1,305 light-years from Earth in the constellation Orion. The new observations of this protostar have helped scientists find a likely connection between the water in the interstellar medium and the water in our solar system by confirming that they have a similar composition.
V883 Ori is a unique protostar whose temperature is so hot that the water in its circumstellar disk has turned to gas, allowing radio astronomers to trace the origin of the water. New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have provided the first confirmation that the water in our solar system may come from the same place as the water in discs surrounding protostars elsewhere in the universe: the interstellar medium. Credit: ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)
“We can think of water’s path through the universe as a trail. We know what the endpoints look like, which is water on planets and in comets, but we wanted to trace that trail back to the origin of water,” said John Tobin, an astronomer at National Science Foundation’s National Radio Astronomy Observatory (NRAO) and lead author of the new paper. “Before now, we could connect Earth with comets and protostars to the interstellar medium, but we couldn’t connect protostars to comets. V883 Ori has changed that and proved that the water molecules in that system and in our solar system have a similar ratio of deuterium to hydrogen.”
Using ALMA, astronomers have discovered the chemical signature of gaseous water in the planet-forming disc V883 Orionis. This acts as a time stamp for the water’s formation so we can track its journey. Credit: TO
It is difficult to observe water in the circumstellar disks around protostars because in most systems water is present in the form of ice. When scientists observe protostars, they look for the water snow or ice line, which is where the water goes from predominantly ice to gas, which radio astronomy can observe in detail. “If the snow line is located too close to the star, there is not enough gaseous water to be easily tracked, and the dusty disk can block much of the water emission. But if the snow line is located further from the star, there is sufficient gaseous water to to be detectable, and that is the case with V883 Ori,” said Tobin, who added that the protostar’s unique state is what has made this project possible.
The V883 Ori’s disk is quite massive and is so hot that the water in it has turned from ice to gas. That makes this protostar an ideal target for studying the growth and evolution of solar systems at radio wavelengths.
Most of the time, water in the circumstellar disks surrounding protostars is in the form of ice, sometimes extending out for long distances from the star. In the case of V883 Ori, the snowline extends 80 au from the star; that’s 80 times the distance between Earth and the Sun, as shown in this animation. But the temperature at V883 Ori is so hot that much of the ice in its disk has turned to gas, enabling radio astronomers to study that water in detail. New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed that the water in V883 Ori’s disc is of the same basic composition as water on objects in our Solar System. This suggests that the water in our own solar system formed billions of years before the Sun in the interstellar medium. Credit: ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)
“This observation highlights the excellent capabilities of the ALMA instrument to help astronomers study something essential to life on Earth: water,” said Joe Pesce, NSF Program Officer for ALMA. “An understanding of the underlying processes that are important to us on Earth, seen in more distant regions of the galaxy, also benefits our knowledge of how nature works in general and the processes that had to occur for our solar system to evolve into what we know. today.”
To link the water in V883 Ori’s protoplanetary disk to that in our own solar system, the team measured its composition using ALMA’s highly sensitive Band 5 (1.6 mm) and Band 6 (1.3 mm) receivers and found that it remains relatively unchanged between each stage of solar system formation: protostar, protoplanetary disc, and comet. “This means that the water in our solar system was formed long before the Sun, planets and comets were formed. We already knew that there is plenty of water ice in the interstellar medium. Our results show that this water was directly incorporated into the solar system during its formation,” said Merel van ‘t ‘Hoff, an astronomer at the University of Michigan and co-author of the paper. “This is exciting as it suggests that other planetary systems should have received large amounts of water as well.”
While searching for the origin of water in our solar system, scientists visited V883 Orionis, a unique protostar located 1,305 light years from Earth. Unlike other protostars, the circumstellar disk surrounding V883 Ori is so hot that the water in it has turned from ice to gas, allowing scientists to study its composition using radio telescopes such as those at the Atacama Large Millimeter /submillimeter Array (ALMA). Radio observations of the protostar revealed water (orange), a dust continuum (green) and molecular gas (blue), suggesting that the water on this protostar is extremely similar to the water on objects in our own solar system and may have similar origins. Credit: ALMA (ESO/NAOJ/NRAO), J. Tobin, B. Saxton (NRAO/AUI/NSF)
Clarifying the role of water in the evolution of comets and planetesimals is crucial to building an understanding of how our own solar system evolved. Although the Sun is thought to have formed in a dense cluster of stars, and V883 Ori is relatively isolated with no nearby stars, the two share one critical thing in common: they both formed in giant molecular clouds.
“It is known that the majority of the water in the interstellar medium is formed as ice on the surfaces of small dust grains in the clouds. When these clouds collapse under their own gravity and form young stars, the water ends up in the disks around them. Eventually the discs evolve and the icy dust grains coagulate to form a new solar system with planets and comets,” said Margot Leemker, an astronomer at Leiden University and co-author of the paper. “We have shown that water produced in the clouds follows this track largely unchanged. So by looking at the water in the V883 Ori disc, we’re essentially looking back in time and seeing what our own solar system looked like when it was much younger.”
V883 Orionis is a protostar located about 1,305 light-years from Earth in the constellation Orion. Credit: ESO/IAU and Sky & Telescope
Tobin added: “Until now, the chain of water in the evolution of our solar system was broken. V883 Ori is the missing link in this case, and we now have an unbroken chain in the lineage of water from comets and protostars to the interstellar medium.”
For more on this discovery, see Water on Earth is even older than our Sun.
Reference: “Deuterium-enriched water binds planet-forming disks to comets and protostars” by John J. Tobin, Merel LR van ‘t Hoff, Margot Leemker, Ewine F. van Dishoeck, Teresa Paneque-Carreño, Kenji Furuya, Daniel Harsono, Magnus V .Persson, L. Ilsedore Cleeves, Patrick D. Sheehan, and Lucas Cieza, 8 Mar. 2023, Nature.
DOI: 10.1038/s41586-022-05676-z