By Ashley Strickland, CNN
(CNN) — Astronomers using radio telescope observations to get an inside look at an interstellar comet have gleaned new insights into when and where the celestial object formed.
The comet, named 3I/ATLAS, gained global attention when researchers first discovered it zipping through our solar system in July. It’s only the third interstellar object, or celestial body that originated outside our solar system, to be spotted passing through our corner of the universe. The comet began its exit of our solar system in December.
Initial research about the comet’s composition, published April 23 in the journal Nature Astronomy, shows that it originated somewhere very different from our own solar system, according to the study authors.
The observations were made using the Atacama Large Millimeter/submillimeter Array, or ALMA, in Chile in early November, just days after the comet passed closest to our sun.
The ALMA radio telescope enabled researchers to measure deuterium within the comet, marking the first time this isotope of hydrogen has been detected in an interstellar object.
“Deuterium is generally found in the water of Solar System comets and in Earth’s oceans in the form of deuterated water, HDO, also called semi-heavy water,” lead study author Luis Eduardo Salazar Manzano, a doctoral candidate in the department of astronomy at the University of Michigan, wrote in an email.
“Our observations with ALMA indicate that the abundance of deuterium in the water of 3I/ATLAS is more than 40 times the value in Earth’s oceans and more than 30 times the value in Solar System comets.”
The findings may allow researchers to better understand the extreme conditions of the comet’s planetary system — and even discern what the Milky Way galaxy was like long before our solar system appeared.
“Interstellar objects are time capsules that bring material from the environments where other planetary systems formed, and our measurements are finally allowing us to open those time capsules and peek at the physical conditions where these objects originated,” Salazar Manzano said.
An ancient and unusual object
Water, or H2O, typically contains two hydrogen atoms and one oxygen atom. The hydrogen atoms include a single proton, or a positively charged subatomic particle. Deuterated water differs slightly in that the hydrogen atoms each also contain a single neutron, or a subatomic particle with no charge. The addition of the neutron means that deuterated water is heavier than H20.
Studying the abundance of deuterated water within 3I/ATLAS can reveal signatures of where the comet formed, the researchers said.
“The enrichment in deuterium generally happens when water forms in cold molecular clouds in interstellar space, which is generally around the same time that solar systems around other stars form,” Salazar Manzano said.
Researchers believe that the planetary system where the interstellar comet originated was incredibly cold, much colder than our own solar system during its formation, he said.
“The temperature in the formation environment of 3I/ATLAS was less than 30 Kelvin, which corresponds to -243.14 Celsius, or -405.67 Fahrenheit,” he said.
Earlier research has indicated that the interstellar comet could be up to 11 billion years old, much older than our solar system or sun, which formed 4.5 billion years ago.
The water still trapped within the comet likely formed long before its host star, but 3I/ATLAS was born afterward from a protoplanetary disk of gas and dust that swirled around the star — the same disk where planets form, Salazar Manzano said.
Given that hotter temperatures can reduce the amount of deuterium due to chemical reactions, the researchers believe that 3I/ATLAS formed and spent most of its time on the outer reaches of the protoplanetary disk, preserving its deuterated water abundance.
The new findings agree with previous observations that found a high abundance of carbon dioxide within the interstellar comet, also consistent with an object that formed in the outer part of a protoplanetary disk.
A historic look at the Milky Way
Using ALMA for observations was key because the radio telescope can point at a closer angle to the sun than traditional telescopes. Radio telescopes detect low-energy radio waves, rather than high-energy visible light or heat that can destroy the optical components of telescopes such as the James Webb Space Telescope.
The team used ALMA to study the comet shortly after it came within 126 million miles of the sun (203 million kilometers)— close enough for the comet’s ice to sublimate as a detectable gas due to the sun’s heat.
The researchers were expecting to spot H20, but it was undetected in 3I/ATLAS.
“This does not mean that 3I/ATLAS did not have ordinary water; it only means that it was below the sensitivity of our observations,” Salazar Manzano said. “However, we got a really big surprise when we realized that we had detected deuterated water despite our non-detection of ordinary water, which told us immediately that 3I/ATLAS was a truly unusual object.”
It’s unlikely that astronomers will be able to determine which planetary system 3I/ATLAS came from, but that doesn’t mean the celestial body won’t provide invaluable insights; interstellar objects can reveal otherwise hidden and unknown aspects about our universe.
The Vera C. Rubin Observatory, located in Chile, released its first images in June and is expected to spot interstellar objects with more frequency — which could enable Salazar Manzano and his colleagues to determine if 3I/ATLAS is an outlier with its deuterated water abundance, or if other such comets contain similar enrichment.
“We’re very clearly only seeing the top of the iceberg when it comes to studying these interstellar comets,” said planetary astronomer Dr. Theodore Kareta, an assistant professor of astrophysics and planetary science at Villanova University near Philadelphia. “Our thinking as a community is evolving rapidly as we learn to ask new questions and make sense of confusing answers.”
Kareta has studied 3I/ATLAS, but he was not involved in this research. The presence of deuterium in the comet is analogous to fingerprints, he said, showing what the comet was essentially born with — as well as what our galaxy was like more than 10 billon years ago when it was less enriched with metals than it is now.
“As our galaxy has gotten older, the kinds of comets it has built over time has changed, and that means that the kinds of planets it can make have changed too,” Kareta wrote in an email. “This is what makes these interstellar comets so interesting — it’s not necessarily what they are or what they look like, but in how they let us look back in time to figure out if the planets ‘out there’ look like the ones we have at home.”
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