‘Oumuamua << oh MOO ah moo ah >> is the unofficial name given to the first object discovered in our solar system known to have originated from a different solar system. Astronomers discovered ‘Oumuamua as it was passing through our solar system in 2017. The object was first sighted by University of Hawaii astronomers at the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observatory. The team that discovered the object gave it the informal name ‘Oumuamua, which means messenger from afar arriving first in the Hawaiian language. The object’s official designation is 1l/2017 U1.
Astronomers originally classified ‘Oumuamua as a comet. However, it did not show some of the common characteristics of comets, such as a gas or dust tail. The astronomers temporarily reclassified the object as an asteroid, though it did not appear to be a typical one. From ‘Oumuamua’s speed and direction, they determined it must have originated outside our solar system.
‘Oumuamua was observed coming from a direction almost directly above the ecliptic plane near the star Vega in the constellation Lyra. The ecliptic plane is the imaginary surface through Earth’s orbit around the sun. ‘Oumuamua was discovered 40 days after its closest approach to the sun. When the object was discovered, it was moving at 196,000 miles per hour (355,431 kilometers per hour)—too fast to be captured into orbit around the sun.
By analyzing its rapidly varying brightness, astronomers determined that ‘Oumuamua has an elongated shape and that it tumbles rapidly through space. They initially estimated it to be from 1,300 feet (400 meters) to 2,600 feet (800 meters) long and from 130 feet (40 meters) to 260 feet (80 meters) wide. ‘Oumuamua’s elongated shape and rapid rotation suggest that it is composed of a dense mixture of metal and rock. ‘Oumuamua is dark and reddish in color, like certain asteroids of the outer solar system that are made up of organic-rich silicates and water ice. Scientists believe the reddish color is produced by the exposure of the surface to cosmic rays over hundreds of millions of years.
Later, scientists observed ‘Oumuamua behaving more like a comet. ‘Oumuamua accelerated slightly as it moved away from the sun. Scientists inferred that this acceleration was caused by unseen gas erupting from ‘Oumuamua on the warm side facing the sun. This gas creates a jetlike force, which is known to modify the orbits of many comets as they get close to the sun. Although the gas emission was not directly observed, astronomers now classify ‘Oumuamua as a weakly active comet. About five years after it was discovered, ‘Oumuamua traveled away from the solar system in the direction of the constellation Pegasus.
‘Oumuamua’s origin is still debated. Some astronomers suggest that it is a fragment of an asteroid or comet that disintegrated as it passed close to a larger object, such as a planet, in a distant solar system. According to this theory, the force of the near-collision ejected the fragment into interstellar space. Another proposed explanation is that ‘Oumuamua is a fragment of a larger nitrogen-ice-rich object, somewhat like Pluto, that was formed by a planetary collision in another solar system. (Pluto has vast deposits of nitrogen ice.) Evaporating nitrogen would accelerate ‘Oumuamua as it moved away from the sun, but the gas would not be visible from Earth. This theory is consistent with the cometlike behavior astronomers observed. Yet another suggestion is that ‘Oumuamua is a relic of an advanced civilization from a distant solar system. According to this idea, the object could be a defunct part of a solar-sail-powered spacecraft, or a probe sent to study and report on Earth’s civilization. The relic theory is held by a minority of scientists.
The discovery of ‘Oumuamua has given scientists new insights into the nature of interstellar space and of planet formation around stars. The detection of ‘Oumuamua suggests that such interstellar objects pass through our solar system frequently. Astronomers believe that the newest powerful telescopes, such as the James Webb Space Telescope, are likely to detect many more objects like ‘Oumuamua. The discovery of ‘Oumuamua also suggests that interstellar space has much more debris left over from planet and star formation than scientists expected.
