A rare visitor from deep space has just completed its closest swing around the sun, and astronomers say the celestial traveler isn’t done fascinating the scientific community just yet. The interstellar comet, officially designated 3I/ATLAS, passed within roughly 126 million miles (203 million kilometers) of the sun in late October, placing it on an outbound trajectory—though it will remain inside our cosmic neighborhood for several more months.
Currently hidden behind the sun from Earth-based observatories, the comet is expected to reappear in the predawn sky around November 11, according to EarthSky. Once visible again, astronomers hope to collect additional data before the object exits our solar system.
No Threat to Earth
While 3I/ATLAS will make its closest approach to Earth on December 19, coming within about 168 million miles (270 million kilometers), the European Space Agency confirms there is no danger to the planet.
The comet is just the third known interstellar object ever observed passing through our solar system, making every captured image and recorded data point increasingly valuable.
Clues Hidden in Ice and Dust
Comets are often described as frozen time capsules—icy fragments left over from the birth of planetary systems. As heat from the sun evaporates their surface material, gases and dust escape, creating the classic glowing tail.
“When it gets closest to the sun, you get the most holistic view of the nucleus possible,” said Darryl Seligman, assistant professor in the Department of Physics and Astronomy at Michigan State University. According to Seligman, measuring the composition of volatile chemicals offers scientists a glimpse into the primordial conditions of the star system where the comet originally formed.
What We’ve Learned So Far
Observations from Hubble, the James Webb Space Telescope, and NASA’s SPHEREx mission detected a mixture of:
Carbon dioxide
Water vapor
Carbon monoxide
Carbonyl sulfide
Water ice
Preliminary research published in August suggests the comet may be 3 to 11 billion years old—far older than our own 4.6-billion-year-old solar system.
Interestingly, carbon dioxide sublimates easily when heated, which implies the comet has never passed close to another star before this encounter.
International Missions Keeping Watch
While the object faded from Earth-based view in early October, space-borne observatories continued monitoring it. On October 3, 3I/ATLAS made a relatively close pass by Mars, coming within 18.6 million miles (30 million kilometers) of the planet and the spacecraft orbiting it.
The ExoMars Trace Gas Orbiter captured a faint white blur—no small feat for a camera designed to survey Martian terrain.
Europe’s JUICE spacecraft (Jupiter Icy Moons Explorer) is also scheduled to make observational attempts in November, although data returns are expected early next year due to slow transmission speeds.
Historic Opportunity
Seligman says astronomers still have several months to monitor activity as the comet travels outward:
“There’s going to be amazing science that comes out,” he noted.
Only two known interstellar objects preceded 3I/ATLAS: ‘Oumuamua (2017) and Comet 2I/Borisov (2019). Each challenged existing theories about planetary formation—and this newcomer promises to do the same.
As the comet drifts back into deep space, it will likely never return—making this a once-in-a-lifetime opportunity for astronomers and stargazers alike.