What is Oumuamua? 6 Fascinating Facts About the First Interstellar Visitor to Our Solar System

In 2017, astronomers made a groundbreaking discovery: the first known interstellar object to pass through our solar system. Named ‘Oumuamua—a Hawaiian word meaning “a messenger from afar arriving first”—this mysterious object has intrigued scientists and the public alike ever since. Here are six key facts about this cosmic visitor.

1. Discovery That Changed Astronomy

Oumuamua was detected on October 19, 2017, by the University of Hawaii’s Pan-STARRS1 telescope. Officially designated 1I/2017 U1 by the International Astronomical Union, it was first classified as an asteroid before further analysis revealed behavior more akin to a comet, due to its unexpected acceleration.

2. Unusual Shape and Speed

Oumuamua is estimated to be up to 400 meters long and unusually elongated—possibly ten times longer than it is wide. Its reddish hue is similar to many distant solar system objects. What stunned astronomers further was its rapid rotation every 7.3 hours and dramatic brightness variations. It was clocked moving at a staggering speed of 196,000 miles per hour (87.3 km/s).

3. A Dry, Mysterious Surface

Unlike typical comets, Oumuamua displayed no visible gas or dust, which left astronomers puzzled. Its dry, metallic or rocky surface lacked the comet-like tail typically seen in icy bodies, leading researchers to suggest it had been bombarded by cosmic rays for millions of years during its interstellar journey.

4. Anomalous Acceleration

After its closest approach to the Sun on September 9, 2017, Oumuamua began accelerating in a way that couldn’t be fully explained by gravity alone. This unexpected movement sparked debate over its true nature—was it a comet, an asteroid, or something entirely different? Though it entered from the direction of the Lyra constellation, its origin remains unknown.

5. Natural Object—or Alien Tech?

Some experts, most notably Harvard astronomer Avi Loeb, suggested Oumuamua could be a piece of alien technology, such as a light sail. While this theory captured the public imagination, the dominant scientific consensus holds that it is a natural object—perhaps a fragment of a hydrogen ice body or a “dark comet” unlike any seen before.

6. A Fleeting Visitor with a Long Legacy

After briefly visiting the inner solar system, Oumuamua is now heading toward the constellation Pegasus, having already passed Mars’s orbit by late 2017. It’s expected to exit the solar system entirely by 2038. Scientists believe such interstellar objects may pass through our solar system roughly once a year, but most remain undetected due to their small size and speed.