Science Blast: First Interstellar Visitor Proves Sneaky Bastard!

Unfortunately, rock proves hard to question…

illustration of'Oumuamua
ALIEN ASTEROID  This artist’s representation of interstellar asteroid ‘Oumuamua shows its unusual shape: 400 meters long and just about 40 meters wide.
No asteroids in the solar system are shaped like that. 

We still don’t know where the first interstellar asteroid came from

 Clues from ‘Oumuamua’s speed and trajectory lead to answers all over the sky map

ISO: A home for a stray space rock. Astronomers are tracking the motions of stars to figure out which one sent an alien asteroid speeding past Earth in October — but they may never find the rock’s true origins.

Officially named ‘Oumuamua, the asteroid was spotted by the Pan-STARRS 1 telescope in Hawaii on October 18 (SN: 11/25/17, p. 14). Its inbound speed of about 25.5 kilometers per second and its slingshot route around the sun pegged it as the first interstellar vagabond ever seen.

That was the easy part. Now astronomers are trying to trace ‘Oumuamua’s path backwards to a particular star or group of stars, without much success. Several papers published online since the asteroid’s flyby peg it as a relatively youthful vagabond, but where it came from is all over the map.

“From my perspective, this object has been hopping stars since it became a free-floating object,” says Simon Portegies Zwart of the Leiden Observatory in the Netherlands. He and his colleagues used star data from the Gaia spacecraft, which released a preliminary catalog of millions of stellar motions in 2016 (SN: 10/15/16, p.16), to calculate the positions of nearby stars in the past. The team found that about 1.3 million years ago, ‘Oumuamua passed within about half a light-year of an unremarkable star called TYC4742-1027-1, it reports on arXiv.org on November 13.

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