The asteroid passed about 15 million miles from Earth earlier this month – and it’s not coming back.

For the first time, a space rock from another solar system has been spotted cruising through our corner of the universe.

The asteroid is about 400 meters across and moving at a clip of nearly 27 miles a second, according to NASA. For months, this interstellar interloper – a fragment of an alien solar system – has been hanging around our cosmic neighborhood. Now it’s zooming away toward another part of the galaxy.

It was first seen on Oct. 19, when a postdoctoral researcher at the University of Hawaii Institute for Astronomy, Rob Weryk, witnessed a small bright object streaking across the sky.

Weryk looked through the archives for the Pan-STARRS telescope, which conducts nightly sky surveys in search of celestial objects moving through the space near Earth, and found the mysterious body in images as far back as early September.

The space rock followed a path like nothing he’d ever seen. Instead of circling around the “ecliptic” – the plane on which planets, asteroids, comets and other solar system objects orbit the sun – this new thing approached from above. It seemed to be coming from the direction of the constellation Lyra and had been cruising through the chilly void of interstellar space at nearly 16 miles a second.

On Sept. 2, it crossed the elliptic plane inside Mercury’s orbit. A week later, it made its closest approach to the sun. Tugged by the sun’s gravity, it reversed course and hurtled back above the elliptic at an angle, passing about 15 million miles from Earth on Oct. 14. It is now headed for the constellation Pegasus.

“This is the most extreme orbit I have ever seen,” said Davide Farnocchia, a scientist at NASA’s Center for Near-Earth Object Studies at the Jet Propulsion Laboratory. “It is going extremely fast and on such a trajectory that we can say with confidence that this object is on its way out of the solar system and not coming back.”