Astronomers monitoring an asteroid warning system had an exciting breakthrough on July 1, 2025, when they detected a large, bright object soaring through the solar system. This discovery sparked global interest among scientists, and by the following day, the European Space Agency confirmed that the object, initially designated as A11pl3Z, is now officially named 3I/ATLAS. Remarkably, 3I/ATLAS is only the third known object to originate from outside our solar system.
Current measurements suggest that 3I/ATLAS has a diameter of approximately 12 miles (20 kilometers). Although its trajectory will not bring it close to Earth, this interstellar object holds potential clues about the formation of planets in solar systems beyond our own and may provide insights into the nature of previous interstellar objects. The day after its discovery, at 3 p.m. EDT, Mary Magnuson, an associate science editor at The Conversation U.S., interviewed Darryl Z. Seligman, an astrophysicist from Michigan State University, who has been studying 3I/ATLAS since its initial detection.
To date, astronomers have identified two other interstellar objects: 'Oumuamua and Comet 2I/Borisov. 'Oumuamua was notable for lacking a dust tail and exhibiting significant nongravitational acceleration, leading to numerous theories regarding its origin. In contrast, Comet 2I/Borisov clearly exhibited characteristics of a comet but had a unique composition compared to other comets within our solar system.
Seligman highlighted that all previous preparations for interstellar objects focused on ones resembling 'Oumuamua or Borisov. However, 3I/ATLAS deviates significantly from both. "This thing doesn't look like either of them," he stated, emphasizing the excitement surrounding this object’s unusual characteristics. With its remarkable brightness and size, 3I/ATLAS is orders of magnitude larger than 'Oumuamua, allowing telescopes to observe it even from a greater distance.
Despite its distance from Earth, 3I/ATLAS is moving at a much faster speed than both 'Oumuamua and Comet 2I/Borisov. Upon waking up to alerts about this object, Seligman anticipated that it might not be interstellar. However, his colleagues quickly confirmed its status as an interstellar object, bringing excitement to the research community.
The identification of interstellar objects relies on the eccentricity of their orbits, which describes how non-circular an orbit is. An eccentricity of zero indicates a perfect circle, while an eccentricity greater than one indicates a hyperbolic orbit, meaning the object is unbound and will not return. This characteristic confirms that such objects did not originate from our solar system.
During observations, astronomers gather points of light from the sky, which do not immediately reveal the distance of the object. Instead, they analyze the object's speed and position against stars in the background to determine its orbit. Fast-moving objects that appear to be hyperbolic are strong candidates for interstellar origins.
Interstellar objects like 3I/ATLAS are considered pristine remnants from the planet formation processes in other solar systems. The knowledge gained from studying small bodies in our solar system has significantly advanced our understanding of planetary formation and evolution. Observations of 3I/ATLAS could provide a new perspective on these processes throughout the galaxy.
As astronomers continue to analyze data, they will work to determine if 3I/ATLAS exhibits characteristics of a comet, such as a cometary tail or unique acceleration patterns. If it is indeed a comet, researchers are particularly interested in its ice content, as this would provide crucial information about its formation conditions. For instance, a high ice content suggests that the object formed far from a star, where ice could remain intact.
With only a few hours of preliminary observations collected so far, the astronomical community anticipates a flurry of activity around 3I/ATLAS in the coming nights. Seligman expressed confidence that nearly every telescope capable of observing the object would be focused on it, promising a deeper understanding of this fascinating interstellar visitor.
