Why an interstellar comet has scientists excited

An ancient comet that entered our solar system this summer is offering a rare opportunity to learn more about distant planetary systems far beyond the reach of any spacecraft, researchers say.

The comet is special both because it is interstellar — meaning it came from outside our solar system — and also because nickel vapor was detected in the gas surrounding the comet.

This comet, called 3I/ATLAS, is only the third such interstellar object to enter our solar system in recorded history. Observing such a rare occurrence is "extremely valuable for us," because it's the only opportunity to look at this object before it moves out of our solar system, said Darryl Z. Seligman, an assistant professor of physics and astronomy at Michigan State University, who is coordinating international teams of scientists that are observing 3I/ATLAS.

Rohan Rahatgaonkar, a Ph.D. student at the Instituto de Astrofísica-Pontificia Universidad Católica de Chile, and Thomas Puzia, who led the team there that made the discovery, were among the authors of a new research paper describing the nickel vapor detection.

The findings are notable because the nickel gas surrounding 3I/ATLAS was detected at a huge distance from the sun (nearly four times Earth's distance from the sun) where temperatures are too cold for metals to normally vaporize, Rahatgaonkar told NPR in an interview.

"It was pretty clear that it was nickel," Puzia said of the data. "So it was super, super exciting."

Puzia cautions that there's still a lot of evidence collection and research to be done into what these findings could mean. But this study into 3I/ATLAS opens the door for new insights into the chemistry of objects and materials that originate far outside of our solar system and are likely billions of years old, he said.

The comet could be older than our solar system

3I/ATLAS was first confirmed on July 1 to be the third interstellar object known to have come into our solar system, in a sky survey by the Asteroid Terrestrial-impact Last Alert System (ATLAS).

When Rahatgaonkar and another student, Baltasar Luco, were set to observe the comet through the Southern Astrophysical Research (or SOAR) Telescope in Chile, they were not looking for nickel vapors.

But over multiple days of observations with the Very Large Telescope in Chile and as 3I/ATLAS continued its journey closer to the sun, Rahatgaonkar and other researchers found that levels of nickel vapor continued to increase.

They measured the nickel using a host of instruments including a spectrograph and by looking at characteristics of the light coming off the comet.

Rahatgaonkar and Puzia also credit a team of researchers around the world, using telescopes and other instruments, for helping to observe and analyze data on the comet.

The analysis of this object is far from over. As it continues its journey close to the sun, it will undergo thermodynamic changes which will cause reactions that could, hopefully, give scientists more clues about where 3I/ATLAS was formed, how it evolved, what it carries and many more potential answers, Puzia said.

This particular interstellar comet "could be maybe older than our solar system," Rahatgaonkar said. The chemical signatures being emitted from 3I/ATLAS "reflect the ancient origin and its long journey through interstellar space."

Rahatgaonkar, Puzia and Seligman emphasized how valuable interstellar objects are to understanding star systems outside of our own solar system. They offer chemical and physical details from those systems and where they formed, potentially billions of years ago.

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