Nearly 4.5 million years ago, two large, hot stars brushed tantalizingly close to Earth’s sun. They left behind a trace in the clouds of gas and dust that swirl just beyond our solar system—almost like the scent of perfume after someone has left the room.

That’s one finding from new research led by Michael Shull, an astrophysicist at the University of Colorado Boulder, and published Nov. 24 in The Astrophysical Journal.

The study sheds new light on the details of Earth’s neighborhood in space.