Interstellar comet 3I/Atlas makes its closest pass by Earth

A stray comet from another star is swinging past Earth this week on its way back to interstellar space. 3I/Atlas will pass within 167 million miles (269 million kilometers) of Earth on Friday, its closest approach on a long tour through the solar system. NASA continues to point its space telescopes at the ice ball, which is estimated to be between 1,444 feet (440 meters) and 3.5 miles (5.6 kilometers) in diameter. The object is fading as it moves away from the sun, so backyard observers with modest telescopes may still catch a glimpse.

The flyby will bring 3I/Atlas somewhat closer to Jupiter in March, when it will pass within 33 million miles (53 million kilometers) of the giant planet. It will be the mid-2030s before it reaches interstellar space again, never to return, said Paul Chodas, director of NASA’s Center for Near Earth Object Studies. The comet is the third known interstellar object to cross the solar system. Interstellar comets like 3I/Atlas originate in other star systems, while home-grown comets like Halley hail from the icy fringes of our solar system.

A telescope in Hawaii discovered the first confirmed interstellar visitor in 2017. Two years later, an interstellar comet was spotted by a Crimean amateur astronomer. NASA’s Atlas telescope in Chile spotted 3I/Atlas in July while surveying for potentially dangerous asteroids. Scientists believe the latest interloper may have originated in a star system much older than ours, making it a tantalizing target for study.

For now the object remains a curiosity rather than a threat. Its passage offers scientists a rare chance to study material formed around another star and to compare it with comets formed in our solar system. The comet’s journey through the solar system is ongoing, and its path tomorrow will continue to be tracked by observatories around the world as it sails back toward interstellar space.