Interstellar comet 3I/ATLAS: a visitor difficult to observe from Earth
Comet 3I/ATLAS, recently observed by the European Space Agency's (ESA) ExoMars Trace Gas Orbiter and Mars Express missions, continues its trajectory toward the inner Solar System. Its passage presents an astronomical event of great scientific interest, although its observation conditions from Earth are very limited.
An interstellar visitor confirmed
3I/ATLAS was discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile. Its hyperbolic orbit indicates that it originates from interstellar space, making it the third such object detected, following 'Oumuamua (2017) and Borisov (2019).
According to orbital calculations published by the Minor Planet Center and ESA, the comet is approaching the Sun at a high angle to the ecliptic plane, meaning it will never be well positioned for prolonged observations from Earth.
Difficulties for ground observation of 3I/ATLAS
At its closest approach to Mars—about 30 million kilometers (18.7 million miles) in early October 2025—Earth is on the opposite side of the Sun, a configuration that prevents direct observation.
Even as the comet moves toward perihelion, it will still maintain a very small solar angle, making it virtually invisible to ground-based telescopes.
Brightness models estimate that 3I/ATLAS will not exceed an apparent magnitude of +14, placing it beyond the reach of most amateur telescopes and only detectable with large-aperture professional equipment under optimal conditions and using automated tracking.
The role of space missions
Meanwhile, the ExoMars and Mars Express probes, located in Martian orbit, have been able to observe the comet without the limitations of solar proximity. Their instruments analyze the composition of the coma and the gas emission, which will allow us to better understand the nature of this interstellar material.
Recommendations for observers
Although 3I/ATLAS will not be visible to the naked eye or with amateur telescopes, astronomers can follow its progress through data published by ESA, the Jet Propulsion Laboratory (JPL), and observatories that manage to record its passage.
For those interested in observing similar phenomena, there are other bright periodic comets that will continue to be excellent targets for telescopes between 150 and 200 mm aperture, especially in dark skies. Keep an eye on our posts to find out which ones they are.
Another event in the history of modern astronomy
The arrival of 3I/ATLAS represents a breakthrough in our understanding of interstellar objects and European science's ability to detect and study them from other planets.
Although it cannot be observed from Earth, its passage will be recorded as an achievement in interplanetary astronomical observation.