Astronomers have made significant strides in understanding the newly discovered interstellar comet, designated 3I/ATLAS. Detected on July 1, 2025, this comet is only the third known object to originate from outside the Solar System. Initial analyses have revealed key differences between 3I/ATLAS and its predecessors, 1I/’Oumuamua and 2I/Borisov, discovered in 2017 and 2019, respectively.
Trajectory and Future Path
Current observations indicate that 3I/ATLAS has been traveling through space at a speed of just under 60 kilometers (37 miles) per second. As it gets closer to the Sun, this speed is expected to increase. The comet was first observed around 4.5 astronomical units from the Sun, which places it inside the orbit of Jupiter.
Its closest approach to the Sun will occur on October 29, 2025, when it will reach about 1.36 astronomical units, just inside the orbit of Mars. In December 2025, 3I/ATLAS will come within 1.8 astronomical units of Earth, providing a unique opportunity for observation.
Origin and Age
The trajectory and speed of 3I/ATLAS suggest that it originated from the thick disk of the Milky Way, known for containing older stellar populations. This region is home to around 15 percent of the galaxy’s stellar mass, predominantly composed of ancient stars.
Astrophysicist Chris Lintott from the University of Oxford highlights the significance of this origin, noting that there is a two-thirds chance that 3I/ATLAS is older than the Solar System itself. Current analyses estimate the comet’s age to be between 3 and 11 billion years, which places it well within the timeline of the universe, which is 13.8 billion years old.
Physical Characteristics
While details about the appearance of 3I/ATLAS remain limited due to its small size and great distance, initial measurements suggest it is considerably larger than both 1I/’Oumuamua and 2I/Borisov, measuring approximately 10 kilometers in diameter. For comparison, 1I/’Oumuamua is thought to be up to 400 meters long, while 2I/Borisov measures around 975 meters.
Observations from the Gemini North telescope have revealed a puffy coma surrounding the comet, which is a cloud of dust and gas. As 3I/ATLAS nears the Sun, it is anticipated that its activity will increase, leading to cometary outgassing. Astronomer Darryl Seligman from Michigan State University suggests that the comet likely contains ices that could become active as it approaches the Sun. However, specific gas emissions must be detected before determining the types and quantities of ice present.
Future Observations and Implications
As astronomers continue to monitor 3I/ATLAS, its size and unique origin provide an excellent opportunity for in-depth study. The comet is expected to yield valuable insights into regions of the galaxy that are typically inaccessible. The implications of this discovery indicate that interstellar visitors may be more common within our Solar System than previously thought.
Looking forward, the ESA/JAXA Comet Interceptor mission, scheduled for launch in 2029, aims to study comets up close. The mission promises to further our understanding of these fascinating cosmic objects and their origins, building on the knowledge gained from 3I/ATLAS.
