`Oumuamua the Interstellar Asteroid
January 4, 2018
Astronomers at the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observatory at the summit of the dormant volcano Haleakala in Hawaii recently detected a mysterious object speeding through our solar system. This by itself was not unusual. One of the main missions of the Pan-STARRS project is to detect near-Earth objects in space that could possibly collide with our planet. However, researchers quickly realized that this space rock did not move like the asteroids and comets they routinely encounter. Astronomers quickly learned that this object was a visitor from beyond our solar system—the first interstellar asteroid ever observed.
This artist’s impression shows `Oumuamua the interstellar asteroid. Credit: ESO/M. Kornmesser
Scientists at NASA’s Center for Near-Earth Object Studies (CNEOS) in Pasadena, California, determined the object was an asteroid, now officially designated as A/2017 UI. Its composition and its unusual path through our solar system showed it was from outer space. Researchers at Pan-STARRS named the asteroid `Oumuamua, which is a Hawaiian word that means messenger.
`Oumuamua appeared only as a faint spot on the Pan-STARRS telescope as it zipped through our solar system at up to 196,000 miles per hour (355,431 kilometers per hour). But later images from other observatories showed that `Oumuamua was 1,300 feet (400 meters) long and about 10 times as long as it was wide, and spinning rapidly. `Oumuamua’s elongated cigar shape is a rarity among space objects. Most asteroids are compact and lumpy after having been battered by countless random collisions with other objects on their long journeys through space. `Oumuamua is also dark red, a color created as its rocky surface was bombarded by high-energy cosmic rays for millions or perhaps billions of years. A/2017 UI traveled in a retrograde orbit (opposite that of the planets) around the sun on its way toward the constellation Pegasus.
Some researchers suggested that `Oumuamua was more than just an interstellar oddity, and that it was perhaps a message from a distant alien civilization. They pointed out that “a cigar or needle shape is the most likely architecture for an interstellar spacecraft, since this would minimize friction and damage from interstellar gas and dust.” Several groups scanned `Oumuamua for alien radio transmissions, including researchers at the Green Bank Telescope in West Virginia, the William Herschel Telescope in Spain’s Canary Islands, and the European Southern Observatory’s Very Large Telescope in Chile. No alien messages were found, and the consensus was that `Oumuamua was odd but completely natural. Scientists suspect that the so-called “space cucumber” has an icy core—as do most comets—beneath its hard carbonic shell.
