ALMA’s radio data revealed unexpectedly high deuterium levels in 3I/ATLAS, hinting the comet formed in extremely cold outer disk regions of another star system.
Using the ALMA radio telescope, astronomers gathered new data about when and where the interstellar comet 3I/ATLAS formed outside our Solar System.
The 3I/ATLAS comet drew the world’s attention during its first pass near the edge of our solar system in July. It is the third interstellar object to cross the boundaries of our galaxy and leave the Solar System; its exit began in December.
The first study of its composition, published on April 23 in Nature Astronomy, points to an origin in a completely different region of space.
Observations began in early November in Chile using ALMA – just a few days after the comet passed its closest approach to the Sun.
Using the radio telescope, scientists were able to measure deuterium in the comet’s water – the first confirmation of this isotope in an interstellar object.
“Deuterium is typically present in the water of Solar System comets and in Earth’s oceans in the form of deuterated water, HDO, also known as heavy water.”
– Luis Eduardo Salazar Manzano
According to the study’s conclusions, the deuterium content in the water of 3I/ATLAS exceeds levels in Earth’s oceans by more than 40 times, and compared with water in Solar System comets – by more than 30 times.
“Our observations with ALMA indicate that the deuterium content in the water of 3I/ATLAS significantly exceeds the corresponding values in Earth’s and interstellar water,” explained one of the study’s key participants, Luis Eduardo Salazar Manzano.
These findings open the possibility of a deeper understanding of the extreme conditions in extrasolar planetary systems – and also allow a glimpse into the past of our Galaxy during the formation of the Solar System.
“Deuterium enrichment usually occurs when water forms in the cold molecular clouds of interstellar space, which is consistent with the timescales of formation of other stars and their planetary systems.”
– Luis Eduardo Salazar Manzano
Scientists believe the origin of this interstellar comet is linked to an extremely cold environment – perhaps from distant regions of a protoplanetary disk around another star where planets typically form.
Estimates suggest the formation temperature of 3I/ATLAS was below 30 Kelvin, indicating exceptionally cold conditions compared with our system at its appearance.
Although it had previously been considered that interstellar comets could be very old, up to 11 billion years, such a discovery continues to broaden our understanding of how worlds form beyond the Solar System. Perhaps 3I/ATLAS formed after the formation of a protoplanetary disk of gas and dust in the same region where planets emerge.
As temperatures rise, the amount of deuterium decreases due to chemical processes, so scientists believe the object formed in the outer regions of the disk, preserving a substantial amount of deuterated water.
New data align with earlier observations of an elevated CO concentration in the composition of the interstellar comet – another sign of an object that formed in the distant parts of the disk.
ALMA played a crucial role: the radio telescope allows capturing low-energy signals, avoiding interference caused by excessive sunlight.
The research group studied the comet after its approach to the Sun at about 203 million kilometers, triggering ice sublimation and gas emission. Signals of water H2O were expected, but they were not detected.
“This does not mean that 3I/ATLAS did not contain ordinary water; it simply was less detectable by our equipment,” noted Salazar Manzano. “However, the signal of deuterated water was a big surprise for us and confirmed that the object is indeed unusual.”
Despite the difficulty in precisely determining the origin of 3I/ATLAS, the object itself may open new horizons in understanding the formation of planetary systems beyond our galaxy.
Further observations with the Vera C. Rubin Observatory in Chile are planned to broaden our understanding of interstellar objects, helping to determine whether they share similarities in their features.
“We will only see the tip of the iceberg in the study of interstellar comets,” noted Dr. Theodore Kareta, assistant professor of astronomy and planetary science at Villanova University. “Our understanding of these objects is evolving rapidly as we pose new questions and seek answers to complex questions.”
Kareta had previously worked on 3I/ATLAS but did not participate in this study. The presence of deuterium in the comet serves as a kind of “fingerprint” of what it formed from – a clue about the state of our Galaxy billions of years ago when metallicity was lower than today.
Thus, interstellar objects open a new chapter in the history of world formation beyond the Solar System and help illuminate the evolution of our galaxy.