3I/ATLAS: Scientific paper details current knowledge about the third interstellar object

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The discovery images of 3I/ATLAS. Credit: ATLAS Chile When reports emerged on July 1, 2025, regarding a new object observed from outside the solar system, the third of its kind identified, astronomers at Michigan State University and an international team collected data on the object. The team prepared a scientific paper detailing current knowledge about the object, named 3I/ATLAS, after NASA's Asteroid Terrestrial-impact Last Alert System (ATLAS). ATLAS consists of four telescopes—two in Hawaii, one in Chile, and one in South Africa—which automatically scan the sky several times nightly for moving objects. The research is published on the arXiv preprint server. Darryl Seligman, assistant professor at Michigan State University and member of the scientific team, led the paper's preparation.

"I heard something about the object before I went to bed, but we didn't have a lot of information yet," Seligman said. "By the time I woke up around 1 a.m., my colleagues, Marco Micheli from the European Southern Observatory and Davide Farnocchia from NASA's Jet Propulsion Laboratory, were emailing me that this was likely for real. I started sending messages telling everyone to turn their telescopes to look at this object and started writing the paper to document what we know to date. We have data coming in from across the globe about this object."

The discovery

Larry Denneau, a member of the ATLAS team, reviewed and submitted the discovery observations from the European Southern Observatory's Very Large Telescope in Chile shortly after the observation on July 1. Denneau said that he was cautious about the finding. > "We have had false alarms in the past about interesting objects, so we know not to get too excited on the first day. But the incoming observations were all consistent, and late that night it looked like we had the real thing. It is especially notable that we found it in the Milky Way in the direction of the galactic center, which is a challenging place to survey for asteroids because of all the stars in the background," Denneau said. "Most other surveys don't look there." John Tonry, another ATLAS member and professor at the University of Hawaii, contributed to the design and construction of ATLAS. Tonry said, > "It's notable every time our work surveying the sky discovers something new, and this comet that has been traveling for millions of years from another star system is of particular scientific interest." Once 3I/ATLAS was confirmed, Seligman and Karen Meech, faculty chair for the Institute for Astronomy at the University of Hawaii, managed communications and worked on compiling data for the paper submission. "Once 3I/ATLAS was identified as likely interstellar, we mobilized rapidly," Meech said. "We activated observing time on major facilities like the Southern Astrophysical Research Telescope and the Gemini Observatory to capture early, high-quality data and build a foundation for detailed follow-up studies." After confirmation of the interstellar object, institutions worldwide began sharing information about 3I/ATLAS with Seligman. 3IATLAS-This diagram shows the trajectory of interstellar comet 3IATLAS as it passes through the solar system. It will make its closest approach to the Sun in October. Credit: NASA/JPL-Caltech

What scientists know about 3I/ATLAS so far

Although data is being collected, the object remains distant from Earth, resulting in several unanswered questions. The scientific team currently knows the following: - It is the third interstellar object detected passing through the solar system. - It may be emitting gas similar to other comets, but this requires confirmation. - It is moving at approximately 60 kilometers per second (134,000 miles per hour) relative to the Sun. - Its orbital path is shaped like a hyperbola. - It has a high apparent brightness. - It is on a trajectory that will exit the solar system and not return, but it will be observable for several months. The James Webb Space Telescope and the Hubble Space Telescope are expected to provide additional information about its size, composition, rotation, and response to solar heating in the coming months. "We have these images of 3I/ATLAS where it's not entirely clear and it looks fuzzier than the other stars in the same image," said James Wray, a professor at Georgia Tech. "But the object is far away and, so, we just don't know." Seligman and his team are studying 3I/ATLAS's brightness to understand the evolution of the coma, a cloud of dust and gas. They are monitoring for changes in brightness and for sudden outburst events. "3I/ATLAS likely contains ices, especially below the surface, and those ices may start to activate as it nears the sun," Seligman said. "But until we detect specific gas emissions, like H₂O, CO or CO₂, we can't say for sure what kinds of ice or how much are there." The discovery of 3I/ATLAS provides new research opportunities. Tessa Frincke, a new doctoral student at MSU, is analyzing data from 3I/ATLAS to predict its trajectory, which may lead to a scientific publication. "I've had to learn a lot quickly, and I was surprised at how many people were involved," said Frincke. [REMOVED: "Discoveries like this have a domino effect that inspires novel engineering and mission planning."] Atsuhiro Yaginuma, a fourth-year undergraduate student on Seligman's team, is investigating the feasibility of launching a spacecraft to approach 3I/ATLAS for imaging and further study. "The closest approach to Earth will be in December," said Yaginuma. "It would require significant fuel and rapid mobilization from people here on Earth. But getting close to an interstellar object could be a rare opportunity." "We can't continue to do this research and experiment with new ideas from Frincke and Yaginuma without federal funding," said Seligman, who is also a postdoctoral fellow of the National Science Foundation. Seligman and Aster Taylor, a former student and current doctoral candidate and 2023 Fannie and John Hertz Foundation Fellow, wrote the following: "At a critical moment, given the current congressional discussions on science funding, 3I/ATLAS also highlights the broader impact of astronomical research. An example like 3I is significant to astronomy—as a science, we are supported almost entirely by government and philanthropic funding. The fact that this science is not funded by commercial enterprise indicates that our field does not provide a financial return on investment, but instead responds to the public's interest in fundamental questions about the universe: Where did we come from? Are we alone? What else is out there? The interest of the public, as expressed by the will of the U.S. Congress and made manifest in the federal budget, is the reason that astronomy exists." More information: Darryl Z. Seligman et al, Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS, arXiv (2025). DOI: 10.48550/arxiv.2507.02757 Journal information: arXiv