Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) made an exciting discovery about the interstellar comet 3I/ATLAS. This comet formed in a much colder part of the Milky Way than where our solar system sits.
For the first time, researchers measured semi-heavy water, or deuterated water, in an object that came from beyond our solar system. Deuterated water has one hydrogen atom replaced by deuterium, a heavier isotope. The study found that 3I/ATLAS contains about 30 times more of this special water than comets born in our solar system.
“Our observations show that conditions for forming planetary systems differ across the galaxy,” said Luis E. Salazar Manzano, the team leader from the University of Michigan. His team focused on 3I/ATLAS when it was closest to the Sun, which ALMA’s unique capabilities allow. Unlike optical telescopes, ALMA can look at the Sun without being blinded by its brightness.
Comets like 3I/ATLAS are often called “dirty snowballs” because of their high water content. This water reveals the chemistry of their birth environment. For solar system comets, this was around 4.6 billion years ago, when our planets were forming. The interesting part? While regular water has a small amount of deuterated water, the ratio in 3I/ATLAS is a staggering 30 times higher. This is also 40 times more than what we have in Earth’s oceans.
This difference in water composition suggests that 3I/ATLAS was created in an unusually cold and chemically distinct region of space. “The processes that create more deuterated water are very temperature-sensitive, needing environments colder than about 30 Kelvin, which is around minus 406 degrees Fahrenheit,” Manzano explained.
The ratios of deuterium and hydrogen in 3I/ATLAS offer a glimpse into its original environment. These elements’ abundances in the universe are believed to have been set during the Big Bang, making this comet a kind of time capsule from its home region. “Each interstellar comet carries a piece of its history,” said Teresa Paneque-Carreño, another team member. “With tools like ALMA, we can start to unravel the conditions of those distant regions and compare them to our own.” This research was published in *Nature Astronomy*.
In recent discussions on social media, space enthusiasts have expressed fascination with what these discoveries mean for our understanding of the universe. The idea that such comets could hold clues about the early cosmos has sparked interest and excitement in both the scientific community and the public. By comparing the findings of comets like 3I/ATLAS with previous observations, scientists hope to learn more about how different environments shape the formation of solar systems in our galaxy.
For more information, you can check the original study published in *Nature Astronomy* [here](https://www.almaobservatory.org/en/press-releases/alma-reveals-interstellar-comet-3i-atlas-formed-in-a-far-colder-world-than-our-own/).
