Astronomers used the Atacama Large Millimeter/submillimeter The object has exceptionally high levels of methanol relative to hydrogen cyanide, differing from most comets originating from Sistema Solar.
Comet 3I/ATLAS was discovered in July 2025 by the ATLAS system, at Chile, and confirmed as the third interstellar object to cross Sistema Solar, after 1I/’Oumuamua and 2I/Borisov. Sua hyperbolic orbit indicates origin outside our planetary system. The measurements focused on organic molecules detected in the coma, the gaseous atmosphere surrounding the nucleus.
Major chemical discovery
The analyzes identified methanol (CH₃OH), a simple organic alcohol, in greater abundance than expected. On two observation dates, the methanol/HCN ratios reached values close to 70 and 120. Esses numbers position 3I/ATLAS among the comets most enriched in methanol ever studied.
Hydrogen cyanide (HCN) appears in smaller proportions. Essa chemical difference suggests formation conditions different from those observed in local comets. Previous Observações with Telescópio Espacial James Webb had already highlighted carbon dioxide dominance in the distant coma.
Differences in release behavior
Methanol arises both from the nucleus and from ice grains in the coma. Esses grains function as secondary sources, sublimating as they approach the Sol and releasing the compound. The Esse pattern occurs in some Sistema Solar comets, but represents a new interstellar object.
HCN comes predominantly from the nucleus. Production appears more uniform, with no significant contribution from coma. Essa distinction was mapped by ALMA’s high resolution, which made it possible to observe different movements of the molecules.
Origins and astronomical implications
The methanol-enriched composition indicates that the comet’s icy material formed under different chemical conditions. Fatores such as low temperature or cosmic radiation in the interstellar medium may have favored this accumulation. The object offers a direct glimpse of another star system.
ALMA captured data on multiple dates between August and October 2025, with heliocentric distances of 2.6 to 1.7 AU. The methanol production rate increased with proximity to Sol. Essa variation reinforces the influence of thermal sublimation.
Details of technical observations
The measurements used ALMA’s Atacama Compact Array to detect faint submillimeter signatures. Observations occurred in multiple pre-perihelion sessions, before the closest point to Sol in October 2025. The results were processed to map molecular distributions in the coma.
Composition compared to other comets
The methanol/HCN ratio in 3I/ATLAS exceeds most solar comets measured at radio frequencies. Apenas comet C/2016 R2 (PanSTARRS) presents similar or higher values. Essa feature highlights the unusual character of the interstellar visitor.
Additional studies continue to explore other compounds in the composition. The presence of organic molecules like methanol connects the object to prebiotic processes in distant environments. Observações Futures may refine the understanding of planetary formation in other systems.
Comet 3I/ATLAS continues to provide valuable data on interstellar chemical diversity. Sua passage allows analysis without the need for external space missions.
