Interstellar Comet 3I/ATLAS Approaches Mars, Observed by Spacecraft

Comet 3I/ATLAS, the third known interstellar object to traverse our solar system, is set to make its closest approach to Mars on October 3, 2025. The comet will pass within approximately 18 million miles (29 million kilometers) of the Red Planet at a velocity of 193,000 mph (310,000 kph).

Discovered in July 2025, 3I/ATLAS has drawn significant interest from the astronomical community. The European Space Agency's Mars orbiters, including Mars Express and the ExoMars Trace Gas Orbiter, are preparing to observe the comet during its flyby. NASA's Mars Reconnaissance Orbiter and surface rovers are also poised to contribute to the observations.

The comet's nucleus is estimated to be between 1,444 feet (440 meters) and 3.5 miles (5.6 kilometers) in diameter. It is expected to reach its closest point to the Sun at the end of October and will pass Earth at a distance of 167 million miles (269 million kilometers) in December.

Observations from the Gemini South telescope in Chile have revealed that 3I/ATLAS's tail is growing, and its coma—a cloud of dust and gas—is expanding as it approaches the Sun. These findings indicate increasing activity as the comet draws closer, although it poses no threat to Earth.

The upcoming observations from Mars-based instruments offer a unique opportunity to study an interstellar object up close, potentially providing valuable insights into the composition and behavior of such rare celestial visitors.