It came from outer space. A cigar-shaped object tumbling end-over-end through the void. The first interstellar asteroid. A rock from a distant star. On October 19, 2017, the Pan-STARRS telescope in Hawaii was searching the sky for killer asteroids when it spotted a faint blur. Its trajectory was like nothing ever seen before. The word went out. High in the Chilean mountains, the Very Large Telescope turned to look. It spied a dark object zooming past the Earth. Its surface was stained deep red by radiation from years of travel between the stars. The Allen Telescope Array listened for radio signals, in case it was an alien artifact. The invader was given a name: Oumuamua. Hawaiian for “scout.” Its shape is like nothing in our own solar system, where objects are more or less round. Oumuamua is ten times longer than it is wide. A tumbling dart, a quarter mile long. It approached from above the plane of the planets, pierced the orbit of Mercury like a bull’s-eye and swung past the sun at 50 miles a second. By the time astronomers noticed it, the asteroid was beyond Earth’s orbit, moving away into the deep night. Oumuamua is dark and receding quickly. It will soon fade from view. Was this stranger among us a fragment from a broken planet? Did some other event shape and fling it toward our star? Oumuamua came from the direction of where Vega is now, but after so long in transit the stars have shifted behind it. We may never know where it came from, or when. Now it is heading outward in the direction of Pegasus, continuing its lonely walkabout through the galaxy. This was our first glimpse of a cosmic vagabond. But not the last. Astronomers think hundreds of comets and asteroids have slipped past us unnoticed, trailing dust and scars of galactic history. We might not be able to explore the galaxy ourselves. But in the fullness of time the galaxy will come to us.