New infrared observations are shedding light on the rare interstellar comet 3I/ATLAS as it bids farewell to our solar system. NASA’s SPHEREx space telescope captured images in December 2025, showing the comet releasing a wave of gas, dust, and complex molecules shortly after getting close to the sun. This unexpected outburst provides scientists with a unique glimpse at materials that formed around other stars.
When SPHEREx observed 3I/ATLAS, it was already moving away from the inner solar system. Instead of fading into the dark, the comet flared up, developing a bright coma filled with water vapor, carbon dioxide, and organic compounds. Its dust tail took on a pear shape due to rocky particles being ejected as the comet became more active.
Carey Lisse, the study’s lead author, noted, “Comet 3I/ATLAS erupted dramatically after its brisk flyby of the sun, causing it to brighten. We observed water ice changing into gas in space.” Discovered in July 2025 by the ATLAS survey, this comet is only the third confirmed interstellar object to pass through our solar system, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. Unlike those, 3I/ATLAS provided an extended chemical show that SPHEREx could uniquely analyze.
SPHEREx studies the universe in infrared light, revealing not only dust but also a detailed mix of molecules streaming off the comet. These include water ice, carbon dioxide, methane, methanol, and cyanide—key ingredients for forming planets. Interestingly, 3I/ATLAS became active well after its closest approach to the sun, suggesting the heat penetrated its surface, triggering a delayed release of ancient ices.
“Comets are about one-third water ice, so 3I/ATLAS was releasing a significant amount of new, carbon-rich material locked deep in its surface,” Lisse added. This analysis gives us a chance to compare our local comets with icy bodies formed around other stars, helping scientists understand if the building blocks for planets and life are common throughout the Milky Way.
As 3I/ATLAS traveled through vast interstellar space, it faced constant bombardment by cosmic rays, likely forming a protective crust. Phil Korngut, a co-author of the study, remarked, “The sun’s energy has now reached deep into the comet, causing the ancient ices to warm and erupt, releasing a mix of chemicals that have been untouched for billions of years.”
This remarkable study, published in February 2026, marks an important contribution to our understanding of interstellar objects and their chemical makeup. By comparing the findings related to 3I/ATLAS with previous comets, scientists can gain insights into the potential for life-sustaining materials existing beyond our solar system.
For further information, you can refer to NASA’s official statement and the study published in the Research Notes of the AAS.
