Astronomers announced the discovery of the object October 26, calling it A/2017 U1. The University of Hawaii team eventually gave it a permanent name of Hawaiian origin, ‘Oumuamua, “a messenger from afar arriving first.” After weeks of follow-up observations, they have released more information about the finding in a new paper, published Monday in Nature, that confirms ‘Oumuamua is the first known interstellar object in our solar system.
‘Oumuamua is a cigar-shaped, 400-meter-long asteroid, red in color, with a surface similar to comets and organic-rich asteroids found elsewhere in our solar system, according to the astronomers. Little is known about its composition. But its existence is, for now, exciting enough.
Astronomers have long predicted this event could happen. Our solar system, in its adolescence, was a turbulent place. As the planets swirled into shape, some of the bigger ones jostled nearby material, sending some of it flying toward the edge of the solar system and beyond. Some of the rejected material could even make its way to another star. Since planet formation is quite uniform across the universe, astronomers believe ‘Oumuamua is one of these outcasts, tossed out of its home system. By this logic, there are likely pieces of our own solar system coasting somewhere in interstellar space or past another star.
Astronomers only had about two weeks after the discovery to observe ‘Oumuamua before it disappeared from the view of optical telescopes. “Because the object is moving fast, and the light we get from it is reflected sunlight, the faster it moves away from both the sun and the Earth, the faster it fades in brightness,” said Karen Meech, an astronomer at the University of Hawaii Institute for Astronomy and the lead author of the paper. She and her colleagues condensed weeks or months of work into days and raced to apply for observation time at the world’s most powerful telescopes, which is competitive and tightly scheduled. Observatories squeezed them in and other colleagues donated time out of their own projects.
Astronomers found that the properties of ‘Oumuamua are unlike any of the approximately 750,000 asteroids or comets known to humanity. “In our simulations, you can see that this could not have been from our solar system—it’s simply going too fast,” said Davide Farnocchia, a navigation engineer at NASA’s Jet Propulsion Laboratory who was responsible for figuring out ‘Oumuamua’s trajectory.
Its orbit was completely different, too, Meech said. Scientists can figure out the shape of the orbit of objects that move around our sun, a measurement known as eccentricity. The eccentricity of all objects bound to the gravity of the sun falls between 0 and 1. The highest known eccentricity, 1.058, belongs to a comet that was discovered in 1980, but astronomers interpret this, along with other measurements that stray from the norm, as the result of objects getting jostled as they moved past giant planets like Jupiter. The eccentricity of the interstellar visitor is nearly 1.2. The difference looks small on paper, but it’s big enough to confirm that ‘Oumuamua doesn’t play by our rules.