Cape Canaveral (US) | A stray comet from another star swings past Earth this week in one last hurrah before racing back toward interstellar space.

Discovered over the summer, the comet known as 3I/Atlas will pass within 167 million miles (269 million kilometres) of our planet on Friday, the closest it gets on its grand tour of the solar system.

NASA continues to aim its space telescopes at the visiting ice ball, estimated to be between 1,444 feet (440 metres) and 3.5 miles (5.6 kilometres) in size. But it's fading as it exits, so now's the time for backyard astronomers to catch it in the night sky with their telescopes.

The comet will come much closer to Jupiter in March, zipping within 33 million miles (53 million kilometres). It will be the mid-2030s before it reaches interstellar space, never to return, said Paul Chodas, director of NASA's Centre for Near Earth Object Studies.

It's the third known interstellar object to cut through our solar system. Interstellar comets like 3I/Atlas originate in star systems elsewhere in the Milky Way, while home-grown comets like Halley's 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 sky-surveying Atlas telescope in Chile spotted comet 3I/Atlas in July while prowling for potentially dangerous asteroids.

Scientists believe the latest interloping comet, also harmless, may have originated in a star system much older than ours, making it a tantalizing target.