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Oumuamua
An artist’s conception shows what the interstellar asteroid ‘Oumuamua might look like. (ESO Illustration / M. Kornmesser)

Update: Scientists say the interstellar asteroid known as ‘Oumuamua is like nothing that’s been seen in the solar system before, with an “extreme oblong shape” that’s as much as 10 times as long as it is wide. The details are laid out in a paper published today by the journal Nature.

Nature’s authors say ‘Oumuamua is relatively dense, possibly with high metal content, lacks significant amounts of water or ice, and shows no signs of dust. They estimate its length to be at least 1,300 feet (400 meters), which is longer than previous estimates.

The size estimate is based on how the light reflected by the object varied over the course of a roughly 7.3-hour rotation period. No direct observations of ‘Oumuamua’s shape could be made, but one can only imagine what conspiracy theorists might come up with.

Previously: An interstellar asteroid has received a name that’s fitting to its status: ‘Oumuamua (“Oh-moo-ah-moo-ah”), a Hawaiian word meaning “a messenger from afar arriving first.”

The first-of-its-kind object forced the International Astronomical Union to come up with a new system for designating small bodies that apparently come from beyond the solar system. Such objects will be given numerical names that contain an “I” for interstellar.  ‘Oumuamua’s designation is 1I/2017 U1.

‘Oumuamua was discovered Oct. 19 using the Pan-STARRS telescope, which is operated near the summit of Maui’s Haleakala volcano by the Institute for Astronomy at the University of Hawaii. The Hawaiian connection adds to the aptness of its name.

The dim object was spotted as it traveled through the inner solar system, at a distance of about 19 million miles from Earth, but an analysis of its trajectory suggests that it came in from a place far beyond the solar system, somewhere in the constellation Lyra. It’s now heading in the direction of the constellation Pegasus.

“This is the most extreme orbit I have ever seen,” Davide Farnocchia, a scientist at NASA’s Center for Near-Earth Object Studies at the Jet Propulsion Laboratory, said in a NASA news release. “It is going extremely fast, and on such a trajectory that we can say with confidence that this object is on its way out of the solar system and not coming back.”

‘Oumuamua appears to be a rotating, pinkish object measuring roughly 100 by 100 by 600 feet (30 by 30 by 180 meters). In a news release, the Institute for Astronomy’s David Jewitt noted that the proportions are “similar to the proportions of a fire extinguisher — although U1 is not as red as that.” Jewett is the principal author of a research paper on ‘Oumuamua submitted to Astrophysical Journal Letters.

It’s unusual for an asteroid to be so highly elongated, sparking speculation that ‘Oumuamua may actually be two less elongated objects in a mutual orbit.

Astronomers are continuing to track ‘Oumuamua’s highly eccentric path in hopes of identifying the planetary system that it may have come from, and perhaps matching its composition to the chemical signature of that potential source.

They don’t expect ‘Oumuamua to remain the only object with an “I.” Still more interstellar interlopers are expected to be discovered, particularly when next-generation observatories such as the Large Synoptic Survey Telescope come online.

“We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems,” said the Institute for Astronomy’s Karen Meech. “What’s most surprising is that we’ve never seen interstellar objects pass through before.”

Meech is the principal author of the paper published in Nature, titled “Discovery and Characterization of the First Known Interstellar Object.” Sixteen other authors contributed to the paper.

This report was initially published at 11:41 a.m. PT Nov. 17.

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