Our solar system teems with millions of asteroids and trillions of comets, left over from the formation of the Sun and planets 4.5 billion years ago. Earth is impacted by small space rocks every day; we see them as “shooting stars,” or meteors. In October 2017, astronomers spotted an unusual object passing through our planetary neighborhood. The object’s size, shape, composition and trajectory hold clues to its interstellar origin.
While it’s the first confirmed object from another solar system, astronomers believe that such objects pass by the Sun at least once per year. Their small size makes these interstellar vagabonds difficult to see.
In a report published in Nature, astronomers at the University of Hawaii’s Institute for Astronomy confirmed that our solar system has a visitor from another star system in our galaxy. Observations from the Pan-STARRS1 telescope reveal the object, classified as “A/2017 U1” and nicknamed “`Oumuamua,” is an asteroid unlike any other yet observed.
“What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically,” team leader Karen Meech said in a statement. “This change in brightness hints that `Oumuamua could be more than 10 times longer than it is wide – something which has never been seen in our own Solar System.”
Of the 750,000 or so known asteroids and comets in our solar system, most are round or oblong and range in size from boulders to small moons. Ceres, the largest object in our solar system’s asteroid belt, has a radius of 476 kilometers and makes up 25% of the entire asteroid belt between Mars and Jupiter. Ceres is one of the thousands of dwarf planets that are scattered throughout the outer solar system.
`Oumuamua, which in Hawaiian means ‘first to reach out,’ is roughly 400 meters long and 40 meters wide. Its reddish tint, according to astronomers, is due to lengthy exposure to cosmic rays as it traveled through interstellar space. “While study of `Oumuamua’s colors shows that this body shares characteristics with both Kuiper Belt objects and organic-rich comets and trojan asteroids,” said Meech, “its hyperbolic orbit says it comes from far beyond.”
Similar coloring is common in objects in our outer solar system, but `Oumuamua’s “unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,” Meech explained.
`Oumuamua’s unusual shape and unique trajectory indicated that it originated around a star other than the Sun. “We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it,” Meech added.
According to the report, `Oumuamua “is compositionally indistinguishable from similar objects in our own solar system despite its curious morphology,” due to its coloring, size, and density. Its trajectory and speed, however, indicate that A/2017 U1 came from outside our solar system.
Some theorized, and no doubt hoped, that the object was an alien ship of some sort, but upon closer observation by West Virginia’s Green Bank Observatory, no evidence that it’s anything but organic space debris was found. Researchers do, however, now believe it may be more of a comet disguised as an asteroid, even though its behavior originally led them to believe it was more likely the latter.
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