CHILE, July 7, 2025
A visitor from afar Unveiling the mysteries of 3I/ATLAS, the largest interstellar object to grace our solar system, offering unprecedented insights into alien star systems.
A massive interstellar comet has been confirmed.
- 3I/ATLAS is the third interstellar object detected, discovered on July 1, 2025.
- It’s significantly larger and brighter than previous interstellar visitors.
- Its trajectory confirms it’s not gravitationally bound to the sun.
- It poses no threat to Earth.
- Scientists hope to learn more about other star systems from it.
The interstellar object designated 3I/ATLAS, is a comet from outside our solar system that astronomers believe can help unlock secrets of other star systems.
How do we know 3I/ATLAS is from another star system?
Astronomers can tell 3I/ATLAS is interstellar because of its path. The object’s trajectory follows a highly hyperbolic orbit, meaning it isn’t held by the sun’s gravity. Its orbital path has an eccentricity of 6.2.
Any object above 1 is on a path that will not loop back around the sun, proving it came from and will return to interstellar space. For comparison, 1I/’Oumuamua, had an eccentricity of about 1.2, and 2I/Borisov came in at 3.6. 3I/ATLAS exceeds both.
How is 3I/ATLAS different from 1I/’Oumuamua and 2I/Borisov?
Besides its hyperbolic nature, its size sets it apart.
“3I/ATLAS is much larger than the other two — it’s about 15 kilometers (km) [9 miles] in diameter, with huge uncertainty, compared to 100m for 1I/’Oumuamua and less than 1km for 2I/Borisov,” said Hainaut. 3I/ATLAS may even be as wide as 12 miles (20 km), though this is still uncertain.
What is 3I/ATLAS?
Like 2I/Borisov, 3I/ATLAS is a comet. After its discovery, it displayed a comet-like coma and tail, resulting in the designation C/2025 N1 (ATLAS), the naming convention for comets.
1I/ʻOumuamua was observed as it departed the solar system, making it hard for astronomers to gather enough data to confirm its nature, which led to speculation it was an alien spaceship. It is likely an asteroid or comet.
Could 3I/ATLAS strike Earth?
Currently, 3I/ATLAS is within Jupiter’s orbit, around 323 million miles (520 million km) from Earth and 420 million miles (670 million km) from the sun.
3I/ATLAS will be approximately 167 million miles (270 million km) from Earth on Dec. 19, and will not pose a threat. On Oct. 2, it will be within 18 million miles (30 million km) of Mars and within 130 million miles (210 million km) of the sun on Oct. 29. At that point it will travel at about 42 miles (68 km) per second, or about 152,000 miles (245,000 km) per hour.
Is 3I/ATLAS visible in the night sky?
Only with certain equipment and patience.
Currently, 3I/ATLAS is in Sagittarius, within the Milky Way, on the southern horizon as seen from mid-northern latitudes in July. It is traveling south around magnitude 18.5, about 2.5 million times fainter than Polaris, according to Gianluca Masi at the Virtual Telescope Project, who imaged 3I/ATLAS on July 3. A 150-200mm/6-8-inch aperture telescope with a CCD camera is needed to image 3I/ATLAS, while an optical telescope needs an aperture of around 400 mm/16-inch.
“It will not be visible to the naked eye, and I think it will be a challenge for an amateur, but some have impressive equipment these days,” Professor Martin Barstow at the School of Physics & Astronomy at the University of Leicester, said.
That may change as it gets closer and brighter. “By the time it makes its closest approach, it will be a relatively easy target for amateur astronomers to observe,” said Norris. At that point, it could reach magnitude 11. For most, 3I/ATLAS will be a science story, not a skywatching opportunity.
When will professional telescopes observe 3I/ATLAS?
Most large observatories are in the Southern Hemisphere, where 3I/ATLAS will be best placed, so images should be shared in the coming days and weeks.
As it nears its bright perihelion, it will be obscured by the sun, so professional astronomers will study it once the bright moon has waned, likely after the last quarter moon on July 18.
More observation is needed, as the data is still preliminary. “It was discovered a few days ago and has been observed only with small telescopes,” said Hainaut. “We are scrambling to get the big guys on it as soon as possible.”
Why is 3I/ATLAS so interesting to astronomers?
Despite the unknowns, it is larger than ʻOumuamua and Borisov, so it is a better target for study.
It is a chance for planetary scientists because interstellar objects connect to other star systems and carry chemical signatures that show how planetary systems form, and maybe even show evidence of life elsewhere.
“They undoubtedly carry chemical signatures from outside the solar system, so gaining observations tells us a lot about the possibility of material traveling between planetary systems,” Barstow said. “If we could get a sample from one, one day, it would be an incredible breakthrough.”
Can we send a spacecraft to intercept or fly by 3I/ATLAS?
It is unlikely, it is too fast.
“We would need a spacecraft ready to do this in space, fully checked out and with a rendezvous capability,” Barstow said.
The need for a spacecraft ready to react to an interstellar object has been considered. The European Space Agency is readying its Comet Interceptor project for launch in 2029 to deal with comets that suddenly appear. “However, even this mission might not be able to cope with the high speed of an interstellar traveler,” Barstow said.
A sample of 3I/ATLAS isn’t possible, it would provide a shortcut for planetary scientists. “Even with our fastest rockets, it would take tens of thousands of years for us to reach nearby stars,” said Norris. “Thanks to these visitors from outside our solar system, we may not have to travel that far to sample star systems beyond our own [but] we’ll need the technology to catch up and reach them before they pass through our solar system.”
Why are astronomers suddenly finding interstellar objects?
It is not a coincidence.
“Clearly, our telescopes don’t affect the outer solar system, so the fact we get more simply reflects that we are getting better at finding them,” Hainaut said.
The Vera C. Rubin Observatory, which released its first images, could discover more interstellar objects like 3I/ATLAS during its decade-long Large Synoptic Survey Telescope (LSST) project. A 2020 paper estimates that around seven interstellar objects could pass within one Earth-sun distance of the sun each year. We haven’t been able to see them until now.
“It will be a dramatic improvement,” Hainaut said of the LSST. “Get ready for 4I, 5I … 42I!”
3I/ATLAS is the brightest and biggest interstellar visitor yet, but it will not be the last.
