International astronomers have made a groundbreaking discovery by detecting atomic nickel vapor in the atmosphere of the interstellar comet 3I/ATLAS. This comet, which is the third of its kind identified in our solar system, was observed on July 20, 2025, at a distance of 3.88 astronomical units (AU) from the Sun. The detection was achieved using the X-shooter and UVES spectrographs at the Very Large Telescope (VLT) located in Chile.
This remarkable finding occurred at low temperatures, where the sublimation of metals is typically not anticipated. The data collected provides valuable insights into the chemical makeup of materials originating from outside our solar system. The comet was initially discovered on July 1, 2025, by the ATLAS system during a standard sky survey and is confirmed to follow a hyperbolic trajectory, indicating its interstellar origin.
During early observations, the comet was recorded in a dormant state, allowing scientists to monitor its activation as it approached the Sun. Subsequent observations revealed an increase in nickel emissions, which became particularly significant on July 23, when the comet was at a distance of 3.78 AU. The measurements indicated a rise in the production of nickel atoms, following a power law where the quantity of nickel (Q(Ni)) is inversely related to the heliocentric distance raised to the power of -6.4.
By mid-August, the comet”s distance from the Sun decreased to 3.07 AU, and cyanogen (CN) was detected at this stage. Interestingly, nickel appeared without any simultaneous detection of iron, with instrumental limits confirming the absence of iron above specified thresholds. The low-temperature processes observed suggest that molecules containing nickel bound to carbon monoxide may disintegrate when exposed to solar radiation.
Observations from the James Webb Space Telescope further enriched the data, revealing that the comet”s coma contains a significantly high proportion of carbon dioxide relative to water. Within the coma, both water ice and carbon monoxide were identified, indicating the presence of frozen materials that originated from outside the solar system.
The analysis involved 11 visits utilizing the X-shooter and two with UVES, with emission intensifying in later observations. The laboratory wavelengths for nickel I were marked with vertical lines, and the regions analyzed included wavelengths from 3210-3255 Å and 3350-3630 Å, displaying a comprehensive array of nickel I transitions.
Comparisons of nickel production against heliocentric distance were plotted, and data from 3I/ATLAS was compared to other comets within the solar system, categorized by dynamic class. Power law fits for 3I indicated exponents of -6.4 and -7.2, with colored symbols representing different comet groups compiled from existing literature. Measurements for 2I/Borisov served as reference points in this analysis.
The approximate surface temperature guided the interpretation of sublimation thresholds. An international team of scientists from Chile, Belgium, the United Kingdom, Canada, New Zealand, the United States, and Italy continues to monitor the comet”s activity. As the comet approaches perihelion, new chemical species are expected to emerge with increasing heat. Ground-based and space telescopes are coordinating efforts to collect data, contributing to research on distant exoplanetary systems.
With its trajectory suggesting a formation billions of years ago, the comet may predate the solar system. The chemical signatures observed reflect the conditions under which these primitive materials were formed, and comparisons with local comets reveal significant variations within the galaxy. The data gathered from 3I/ATLAS will enhance our understanding of the building blocks of planetary formation.
