Interstellar asteroid 'Oumuamua may actually be made of ice

Spectroscopic analysis of 'Oumuamua, suggests the surface behaves similarly to comet ices.

By Brooks Hays
Interstellar asteroid 'Oumuamua may actually be made of ice
New analysis of the first-ever observed interstellar object suggests the traveller is made of ice. Photo by ESO/M. Kornmesser

Dec. 19 (UPI) -- New analysis of 'Oumuamua, the first interstellar object to visit our solar system, suggests the cigar-shaped traveler is made of ice, not rock.

When scientists first spotted the oddly-shaped orb, they realized its trajectory placed its origin outside the solar system. Though the first of its kind, researchers assumed a comet would be the most likely interstellar visitor.


But when it passed by the sun, it showed no signs of melting. As a result, some scientists concluded the orb must be an asteroid.

During its brief trip through our solar system and past the sun, researchers were able to train several telescopes on the object.

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New analysis of data collected by Very Large Telescope in Chile and the William Herschel Telescope in La Palma, Spain, suggests the object's spectral properties are similar to those of a comet.

Spectroscopy involves the breakdown of light reflected and absorbed by an object into individual wavelengths. The breakdown yields spectral signatures that reveal an object's chemical composition.

While much of the surface of the interstellar object appears red under visible light, infrared light casts the orb in grey tones. Spectroscopic analysis of 'Oumuamua suggests the surface behaves similarly to comet ices.


Over time, cosmic radiation can try out a comet's surface ices and trigger chemical reactions that cause the formation of a crust of carbon-based compounds.

"So although 'Oumuamua appeared as an asteroid-like point of light in our telescopes, it may be icy in its interior," Alan Fitzsimmons, an astrophysicist at Queen's University Belfast, wrote in The Conversation. "And its insulating red rock-like surface could be the consequence of its lonely journey between the stars."

The latest findings -- detailed in the journal Nature Astronomy -- explain why interstellar objects haven't been spotted until now. They're hard to see. Scientists have known asteroids and comets are likely to visit from afar, but their dark coatings camouflage them.

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"In some ways we had expected these things for some time," Michele Bannister, an astronomer at Queen's University Belfast, told the Independent. "Our own solar system has ejected millions of very small rocky bodies,and so we should expect that others do the same."

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