Interstellar Comet 3I/ATLAS

The appearance of the interstellar comet 3I/ATLAS has opened a new chapter in the study of space comets and cosmic bodies travelling through the universe. This rare interstellar comet brightened remarkably as it moved behind the Sun in October 2025, allowing astronomers to explore the mysteries of deep space objects entering our solar system.

Through advanced observation methods and space missions, scientists gathered key data about the behaviour, trajectory, and composition of this extraordinary interstellar visitor from outer space.

Discovery and Nature of the Interstellar Comet

An interstellar comet is a cosmic body that does not belong to our solar system. It travels on a hyperbolic trajectory, indicating that it originated from another star system. Unlike solar system comets, which orbit the Sun, an interstellar comet passes through our system only once before heading back into deep space.

The first known example was interstellar comet Borisov in 2019, followed by interstellar comet 3I/ATLAS, which was closely observed as it approached perihelion—its closest distance to the Sun—on 29 October 2025.

This rare comet passing through the solar system showed a rapid increase in brightness as solar radiation activated volatile materials on its surface, making it one of the most scientifically valuable interstellar objects discovered to date.

Spacecraft Tracking and Observation

• During its behind-the-Sun passage, the interstellar comet 3I/ATLAS was unobservable from Earth-based telescopes. However, several space missions, including NOAA’s GOES-19 (CCOR-1), NASA-ESA’s SOHO (LASCO C3), and NASA’s PUNCH mission, were used for tracking interstellar comets with spacecraft.

• These observatories utilized coronagraphs, which block the Sun’s glare to reveal faint nearby structures — a technique crucial for comet observation when the object is too close to the Sun.

Through these efforts, scientists obtained continuous data about the interstellar comet’s trajectory, brightness, and activity levels. Such space missions studying interstellar comets offer valuable insights into how comets from beyond interact with the Sun and how their materials behave under intense heat.

Brightening Near Perihelion

• As the interstellar comet 3I/ATLAS approached the Sun, its brightness rose from magnitude 11 to around magnitude 9.

• Although it remained invisible to the naked eye, the comet brightening near the Sun was clearly captured by space-based instruments.

• This behaviour occurs when solar heat triggers sublimation—gas and dust escaping from the comet’s nucleus—creating a glowing coma and a faint tail.

• Such phenomena are critical for understanding the physical structure of an interstellar comet and how it differs from regular solar system comets.

• The perihelion of the interstellar comet also revealed dynamic outflows, dust formation, and volatile activity that can help scientists decode its chemical composition and origin.

Scientific Importance

• Studying an interstellar comet like 3I/ATLAS provides rare clues about other star systems and how planetary bodies form. By comparing interstellar comets Borisov and 3I/ATLAS, scientists can analyse differences in dust composition, volatile content, and nucleus behaviour.

• Such comparisons are essential for understanding the diversity of interstellar objects that travel through our solar neighbourhood.

• The data obtained from NASA and ESA missions—particularly SOHO and PUNCH—enhance our understanding of how spacecraft are used to track interstellar comets near perihelion.

• These findings contribute to the growing field of comet astronomy and help explain the role of interstellar comets in revealing the early processes that shaped the solar system’s origins and cosmic evolution.

Key Exam-Oriented Facts

• 3I/ATLAS is an interstellar comet, meaning it originated beyond the solar system.

• Perihelion date: 29 October 2025, during a behind-the-Sun passage.

• Spacecraft used: GOES-19 (CCOR-1), SOHO (LASCO C3), and NASA’s PUNCH mission.

• Brightness change: from magnitude ~11 to ~9 near perihelion.

• Observation instruments: coronagraphs and heliophysics spacecraft.

• Scientific value: Helps understand composition, dust release, and dynamics of interstellar objects.

• Comparison: Similar in nature to interstellar comet Borisov (2019).

• Observation type: Space-based comet observation using coronagraphs and wide-field imagers.

Final Thoughts

The interstellar comet 3I/ATLAS is a rare cosmic visitor that originated outside our solar system and recently brightened as it passed behind the Sun in October 2025.

Tracked by spacecraft such as NASA’s SOHO, PUNCH, and NOAA’s GOES-19, the comet’s activity was captured using coronagraph imagery, as it was invisible from Earth. Scientists observed a rise in brightness near perihelion, suggesting increased gas and dust release caused by solar heating.

The study of interstellar comets like 3I/ATLAS offers vital clues about the formation of planetary systems, the nature of deep space objects, and the chemical diversity of materials travelling through our galaxy.