First interstellar visitor described as an 'oddball'


The International Astronomical Union, which is responsible for cataloging the names of space objects, also gave the asteroid its very first "I" for "interstellar" designation, which shifts its formal name from A/2017 U1 (with the "A" standing for "asteroid") to "1I/2017 U1".

"For decades we've theorised that such interstellar objects are out there, and now - for the first time - we have direct evidence they exist", said Thomas Zurbuchen, associate administrator for Nasa's science mission directorate in Washington DC. "This history-making discovery is opening a new window to study formation of solar systems beyond our own".

Apparently, unlike many asteroids, 'Oumuamua doesn't have an icy tail behind it - possibly thanks to its spinning trajectory. This unique object was discovered on October 19, 2017 by the Pan-STARRS 1 telescope in Hawaii. Gemini, the ESO's Very Large Telescope in Chile, the Canada France Hawaii Telescope, the United Kingdom Infrared Telescope, and other observatories trained their eyes on the asteroid.

'Oumuamua is not the first interstellar object to reach the solar system, or the last; NASA estimates that one flies by per year. Astronomers are now revealing more details about the interstellar interloper and it's just plain weird. In fact, it's like nothing we've ever seen before. An artist's impression shows a very elongated shape, different from any known asteroids. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving asteroid.

Putting the pieces of these observation together, astronomers concluded that the asteroid is like nothing they've ever seen before.

Image by NASA
Image by NASA

The study, titled "A Brief Visit From a Red and Extremely Elongated Interstellar Asteroid", appeared today (Nov. 20th) in the scientific journal Nature.

The VLT's FORS instrument was able to make very precise spectroscopic measurements of 'Oumuamua's brightness and color.

Karen Meech explains the significance: "This 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".

"We also found that it has a dark red color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it", Meech, one of the authors of the new study, added. Light-curve observations indicate that the object has an extreme oblong shape, with a 10:1 axis ratio and a mean radius of 102±4 m, assuming an albedo of 0.04. Apparently, this asteroid is long and skinny, much like a cigar, and is spinning constantly as it travels, as if some otherworldly explosion or cataclysmic event picked up the little rock and tossed it out across the galaxy like a big throwing knife. It's dark and reddened surface is also an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years.

Led by Dr. Meech, the team included members from the European Southern Observatory, the Osservatorio Astronomico di Roma, the European Space Agency's SSA-NEO Coordination Center, and the Institute for Astronomy at the University of Hawaii in Honolulu.

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