Earliest images of interstellar object suggest alien solar system origins

Astronomers have disclosed new images of the interstellar object known as 3I/ATLAS that were captured months before its official discovery, indicating the object was releasing gas well outside Earth’s orbit — roughly six times the distance between the Sun and Earth, or about 558 million miles. The finding adds to the evidence that 3I/ATLAS originated in a solar system different from our own and carries a chemical signature distinct from typical comets seen in our neighborhood. While the prevailing view among scientists remains that 3I/ATLAS is an interstellar comet, not an artificial craft, the prediscovery data illuminate how materials from other stars may form and evolve before entering another system.

Researchers from Michigan State University examined archived observations from NASA's Transiting Exoplanet Survey Satellite, or TESS, and identified clues of 3I/ATLAS two months before the object was officially discovered on July 1, 2025. The TESS images, taken between May 7 and June 2, show the object tracing a path that aligns with the plane along which planets in our solar system orbit the Sun, enabling scientists to search their datasets for earlier sightings. In those prediscovery images, 3I/ATLAS appeared brighter than expected, a signal that it may have been releasing gases or dust well before it began its approach toward the Sun.

The study, published in the Astrophysical Journal Letters, notes that 3I/ATLAS already showed a tail while still far from the Sun, suggesting activation in the outer solar system, near Saturn. The presence of a tail at such distances implies the object was shedding material early, potentially due to intrinsic heat or chemical processes that differ from those in comets native to our own solar system. Co-author John Noonan, a postdoctoral fellow at Auburn University, emphasized the importance of compiling observations from this prediscovery window. He said that capturing observations from a period when the object was present in telescope data but not yet recognized is essential to understanding how interstellar visitors turn on as they near a star. Noonan cautioned that 3I/ATLAS may respond to solar heating in ways unlike regular comets, reinforcing the idea that this object formed in a fundamentally different environment.

The researchers propose that the distinct outgassing pattern could reflect a solar system that formed under different conditions, possibly with a larger share of carbon-based ices that vaporize at cooler temperatures. Such chemistry could produce gases not typically seen in comets from within our solar system. They suggest that molecules like carbon monoxide, an odorless gas associated with burning wood or fossil fuels on Earth, could be present in higher abundance in 3I/ATLAS and contribute to the unusual activity observed far from the Sun. Adina Feinstein, an assistant professor of physics and astronomy at MSU, described the finding as providing a rare glimpse into another planetary birthplace. Feinstein said, 3I/ATLAS gives us an opportunity to study other solar systems up close and personal, without actually needing to visit them.

The team notes that the differences in composition and activity could reflect the broader diversity of exoplanetary systems. If 3I/ATLAS originates from a solar system with different formation conditions, its building blocks may include a higher fraction of carbon-rich ices that become volatile at lower temperatures, reshaping expectations about how such objects behave as they travel through interstellar space and eventually pass through other stars, including our own. These findings contribute to a growing understanding that interstellar visitors can carry chemical fingerprints that illuminate the variety of planet-forming environments across the galaxy.

Astronomers stress that while these early indicators are provocative, the object remains a natural body and not a piece of extraterrestrial technology. The consensus in the field is that 3I/ATLAS is an interstellar comet, a relic of another star system that crossed our own, but the difference in its early activity underscores the value of studying such travelers to learn about the potential diversity of planetary materials. The study adds a notable datapoint in a broader effort to characterize how interstellar objects form, migrate, and evolve, offering a more complete picture of the cosmos and of the processes that seed planetary systems.

Looking ahead, 3I/ATLAS is slated to make its closest approach to Mars on October 3, with its nearest approach to Earth expected on December 17, when it will be about 223 million miles away. Observatories around the world will have renewed opportunities to monitor its trajectory, brightness, and any changes in its tail as it moves away from the inner solar system. The ongoing monitoring of interstellar objects — including the reanalysis of archival data from missions like TESS — remains a key tool for researchers seeking to map the diversity of objects that travel through our cosmic neighborhood. In this context, the prediscovery observations of 3I/ATLAS offer a tangible hint of how alien solar systems might imprint their own distinctive chemistry on the small bodies that wander into another star’s influence, expanding humanity’s understanding of where the building blocks of planets and life may originate.