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This artist’s impression shows the first interstellar asteroid: `Oumuamua. Photo by M. Kornmesser

This asteroid is our solar system’s first known ‘alien’ visitor

Our solar system has never received any visitors that we’ve been able to detect — until now. About a month ago, astronomers noticed a fast-moving, rocky asteroid hurtling through our solar system. To the astronomers’ surprise, this was our solar system’s first known “alien” encounter, and on November 20, they described the mysterious passerby in Nature Letters.

They named the asteroid A/2017 U1 or ‘Oumuamua (pronounced “Oh-moo-uh-moo-uh”) which means “a messenger from the past.”

How do scientists know “Oumuamua” is an interstellar voyager? In our solar system, all orbiting bodies follow mostly elliptical or sometimes spherical paths around the sun. But in ‘Oumuamua’s case, its path was hyperbolic–a big ‘U’ shape. Basically, astronomers followed its path into our system and saw that it was much faster than any of our asteroids. And as it sped around the sun, it got slung right back out of here.

Also, while most planets, dwarf planets and comets orbit along the same plane — like hula hoops around the sun’s “waistband” — ‘Oumuamua swung around the sun and its closest planets like a giant boomerang from above.

‘Oumuamua swung around the sun and its closest planets like a giant boomerang from above. Photo by NASA/JPL

‘Oumuamua swung around the sun and its closest planets like a giant boomerang from above. Photo by NASA/JPL

‘Oumuamua looks weird. First spotted on the Pan-STARRS1 telescope by a team at the University of Hawaii, ‘Oumuamua is nothing like we’ve ever seen before. It is an unusual, oblong asteroid with a radius of nearly 330 feet and about a quarter-mile long. Picture a cigar or baseball bat speeding through space.

The astronomers figured out its elongated shape when they noticed its brightness varied when it rotated every 7.3 hours. When the asteroid’s long side faced the Earth, more of its surface area could reflect sunlight, making it more visible to us. And when the tip of the rock faced us, it was a very dim point of light.

“What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically,” planetary astronomer Karen Meech, who led the University of Hawaii team, said in a statement. “This change in brightness hints that ‘Oumuamua could be more than 10 times longer than it is wide — something that has never been seen in our own solar system.”

What is it made of? The asteroid has a reddish hue, and astronomers reported that this redness resembles some of our comets and asteroids. That color, they noted, is likely from metallic and carbon-rich matter — some of the fundamental ingredients of life. But even though the asteroid shares this characteristic with our solar system’s objects, ”its hyperbolic orbit says it comes from far beyond,” Meech said.

Where did it come from, where did it go? No one knows for sure, but astronomers believe it roughly came from the direction of Vega in the constellation Lyra. The team will continue following ‘Oumuamua and find out its path to and from us.

But Meech and her colleagues now realize that asteroids come in all kinds of shapes and sizes. This means, next time, astronomers shouldn’t gloss over the strange and quirky because they may be far more interesting than we once thought.

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