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

‘Oumuamua, the alien asteroid, wears an organic coat. But what’s inside?

Remember ‘Oumuamua? It is the interstellar asteroid that boomeranged through our solar system a couple months ago. Though its visit lasted a matter of weeks, astronomers had just enough time to frantically gather tons of data about the mysterious, fast-fleeing object.

In the latest ‘Oumuamua update, published Monday in Nature Astronomy, one research team deciphers the chemical makeup of the cigar-shaped rock. They found striking similarities between ‘Oumuamua to icy asteroids in our own solar system. ‘Oumuamua’s exterior also consists of an insulating organic-rich material, which might protect any ice that exists within.

What did the scientists do? Planetary scientists predicted in the past that interstellar objects would most likely be made of ice, like a comet, said Alan Fitzsimmons, an astronomer at Queen’s University Belfast in the U.K. and lead author of this study.

“In laboratory experiments from as early as the 1980s and 1990s, we’ve learned that objects in our solar system lose ice when they orbit close to the sun,” Fitzsimmons explained. “The experiments show that when you take a mixture which has both water ice and carbon-based ice, the ice streams away and you’re left with this dry, carbon-rich organic residue.”

Once ‘Oumuamua appeared, Fitzsimmons’ team developed new models and conducted spectral analysis–a method using light to determine the asteroid’s chemical composition — via the William Herschel Telescope in Spain and the Very Large Telescope in Chile. Elements and compounds reflect different patterns of light, which spectral analysis can identify.

“So the light patterns on ‘Oumuamua were very similar to ice-bearing bodies we see in the outer part of the solar system,” Fitzsimmons said. “Once we get away from Jupiter and deep into the Oort Cloud, we see lots of asteroids that look like this one, including the exterior organic-rich surface.”

An artist’s concept shows the interstellar asteroid `Oumuamua. Video by M. Kornmesser

What they found: But ‘Oumuamua’s outer coat still has some differences relative to free-floating bodies from our solar system. Unlike a comet, ‘Oumuamua didn’t develop a long, icy tail when it swung dangerously close — within 23 million miles — to our sun in early September. Even though at that distance, the asteroid heated up to more than 570 degrees Fahrenheit. Any surface ice would have been vaporized, creating a tail, yet this asteroid seemed totally dried out.

Ice or no ice, why should we care? For millions (maybe even billions) of years, this asteroid traversed the universe as cosmic rays bombarded it. These rays are streams of high-energy particles that come from stellar sources, such as pulsars or supernovae. They shaped ‘Oumuamua into what it is today.

This extremely long-term cosmic ray exposure could mean the asteroid is much older than anything in our solar system, the research team noted. Over this period, ‘Oumuamua slowly dried out and hardened into a half-meter thick crust.

“Now we don’t know how long this object has been out there, but these experiments imply that if you’re out there for about 100 million years, you can form a crust somewhere between half a meter and a couple of meters thick around the surface,” Fitzsimmons said. “And that could be solid protection for any water-rich ice tightly packed inside.”

Astronomers hypothesize that ice, possibly made of water, may still linger somewhere inside ‘Oumuamua, or ice existed potentially on this spacefarer throughout its past. If either of these is the case, then the icy orbs dwelling in our solar system — comets and asteroids — may not be so special after all, scientists report.

“Mother Nature may have a particular recipe for making these small bodies,” Fitzsimmons said. “And that recipe may not vary too much as you go from place to place throughout our galaxy.”

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