3I/ATLAS: Interstellar comet has water unlike any in our solar system

The interstellar comet 3I/ATLAS harbors water and carbon molecules at unprecedented levels for our solar system, hinting that it originated around a distinctly different and much older star than the sun.

Since its entry into our solar system last year, astronomers have closely monitored 3I/ATLAS, which exhibits unusual characteristics. It contains significantly more carbon dioxide and water than most other comets observed, with preliminary age estimates suggesting it is about 8 billion years old, nearly twice the age of the sun.

Recently, Martin Cordiner from NASA’s Goddard Space Flight Center in Maryland, alongside his team, discovered that the comet’s deuterium levels—a hydrogen isotope with an extra neutron—are at least ten times greater than those found in any previously studied comet.

While deuterium is naturally found in small quantities in Earth’s oceans, 3I/ATLAS has more than 40 times the typical amount. “3I/ATLAS continues to astonish us with its insights into the similarities and differences between its host system and our solar system,” Cordiner comments. His team utilized the James Webb Space Telescope for these observations.

“It’s truly remarkable,” says Paul Hartogh from the Max Planck Institute for Solar System Research in Germany. “This deuterium-to-hydrogen ratio in water is extremely unusual, and nobody would have expected this.”

Typically, such elevated deuterium levels are found only in the coldest regions of the Milky Way, notes Ewine van Dishoeck at Leiden Observatory in the Netherlands. “That suggests it’s likely from the very outer part of the disc around its original star, making it easier for it to be ejected,” Dishoeck explains.

Cordiner and his team also detected relatively low amounts of carbon-13—a carbon isotope usually formed after supernova explosions. The presence of low carbon-13 levels, also observed in young star-forming clouds, indicates that 3I/ATLAS may have formed in a period of the galaxy’s history with fewer supernovae. This implies the comet might have originated around a star system aged between 10 billion and 12 billion years, more than twice the age of the sun, according to Cordiner.

Nonetheless, Dishoeck points out that the precision of the carbon measurements limits the certainty regarding its age.