CATA astronomers reveal surprising data on interstellar object 3I/ATLAS

Like a bottle thrown into the cosmic ocean and washed up on our shores, the interstellar object 3I/ATLAS has brought with it chemical messages from another star system. Thanks to observations made with ESO's Very Large Telescope (VLT) in Chile, a team of astronomers from CATA detected unexpected emissions of nickel and cyanogen at great distances from the Sun. With no iron emissions, this behavior, never before seen in comets, provides new clues about the formation of these bodies around other stars.

Recent research conducted by members of the Center for Astrophysics and Related Technologies (CATA) and the Institute of Astrophysics at the Pontifical Catholic University of Chile has revealed new data on the interstellar object 3I/ATLAS, detailing surprising characteristics in its composition.

The study titled, ”VLT observations of interstellar comet 3I/ATLAS II. From quiescence to glow: Dramatic rise of Ni I emission and incipient CN outgassing at large heliocentric distances It is led by CATA students Rohan Rahatgaonkar, Juan Pablo Carvajal, and Baltasar Luco, under the direction of CATA Principal Investigator and UC Institute of Astrophysics professor, Thomas Puzia.

Thanks to the spectrographs X-SHOOTER and UVES on ESO’s Very Large Telescope (VLT) in Chile, astronomers analyzed its light as 3I/ATLAS traveled between 4.4 and 2.85 astronomical units from the Sun. The results show a spectrum dominated by reddish dust, accompanied by first detections of atomic nickel (Ni I) and cyanogen (CN).

This is the third interstellar object to visit our solar system, after 1I/‘Oumuamua and 2I/Borisov. However, unlike them, 3I/ATLAS seems to mix familiar characteristics with unexpected behaviors. Although its exact size remains a mystery, it already shows the characteristics of a comet, a bright coma, and the beginning of a tail. “This object is telling us its story long before it approaches the Sun, revealing the exact order in which chemical signals emerge during its visit to our neighborhood,” notes Thomas Puzia, Principal Investigator at CATA.

For Rohan Rahatgaonkar, a doctoral student at CATA, this finding is particularly significant. “This is the first time we have seen such an active interstellar comet from so far away. It’s like reading the prologue of a book before it reaches the climax of the story at perihelion (the point closest to the Sun).”

The mystery of iron-free nickel

Normally, as comets approach the Sun, the heat causes water and other ices such as carbon dioxide and carbon monoxide to evaporate, releasing gases that form the typical coma. But 3I/ATLAS decided to break the rules: it did not show these compound gases, but it did release nickel atoms, a metal never before detected in this way at such a great distance from the Sun and without signs of iron, which, in previous objects such as 2I/Borisov, was usually observed simultaneously.

“It’s as if this comet first ignited the metallic notes of an orchestra, but without the usual instruments of water or CO sounding,” says Puzia. “The fact that nickel was seen so early and alone could indicate that it formed and persisted in extreme environments, perhaps in the thick disk of the Milky Way.”

Doctoral student Juan Pablo Carvajal adds: “In comets in the Solar System and in the previous interstellar object 2I/Borisov, nickel had always been observed alongside iron. Here we see it activated on its own, as the first sign of a cryogenic fossil from billions of years ago. That tells us about a different process; about a natural laboratory unlike any other we know.”

Next steps: the big date with the Sun

On October 29, 3I/ATLAS will reach its perihelion. The CATA and UC team already has a 37.5-hour observation program with the VLT to continue studying its spectrum, as well as an additional project with very high-resolution instruments that will allow its isotopic composition to be measured.

“The coming weeks will be like opening more pages of this interstellar manuscript. Each new piece of data will allow us to reconstruct how and where this object was born, and better understand how comets and planets form around other stars,” concludes Puzia.

Baltasar Luco, a master’s student at UC and affiliated member of CATA, concludes by adding that “so far, we have only read one chapter of the electromagnetic spectrum. What is coming from our Institute promises to reveal even more mysteries of this cosmic traveler.”