‘Ouamuamua, the first observed interstellar object, zipped through our solar system back in October 2017 -- and astronomers have been trying to understand it ever since. 

While some researchers speculated it could be a comet, asteroid, or even an alien-spacecraft, researchers at Arizona State University are now suggesting this “oddball” structure moving along at 196,000 miles per hour could possibly be a nitrogen-based fragment of a Pluto-like planet from another solar system. 

However, Darryl Seligman, astrophysicist at the University of Chicago and author of multiple papers about the object, says that while that theory isn’t entirely impossible, ‘Oumuamua's young age makes it more likely to be a hydrogen iceberg born inside giant molecular clouds in space – although a nitrogen-based object is not entirely out of the question.  

“’Oumuamua is likely only around 40 million years old, which is young for an interstellar object. An object from a planetary system, like a Pluto-like planet, would probably be much older than that, and it would have been moving much faster at that old age,” Seligman said, because the older an object in space is, the faster it tends to move. “But ‘Oumuamua was moving so slowly in the galaxy that our solar system basically smashed into it, not the other way around. If ‘Oumuamua came from a pre-stellar core in a molecular cloud, then that would explain its slow speed and its young age, because giant molecular clouds don’t live very long before they disappear.”  

In a paper published in Astrophysical Journal Letters, Seligman said molecular clouds, which are massive stellar nurseries, can stretch for light-years and contain enough gas to form tens of thousands of stars. But they might also spit out hydrogen icebergs that look and behave a lot like ‘Oumuamua. 

Yale Scientist Garrett Levine says that ‘Oumuamua's correlated motion with the Carina and Columba stellar association, two potential nearby birthplaces, make hydrogen a stronger possibility.

“Nitrogen ice could explain `Oumuamua's as generic to a class of objects. However, while solid N2 exists even in our Solar System on Pluto-like objects, the potential galactic reservoir is much smaller than that of hydrogen ice,” Levine said. 

The only way to know for certain, however, would be an interception mission, which Seligman proposed in a 2018 paper, and is currently being considered by NASA and the European Space Agency’s (ESA) Comet Interceptor which is scheduled to fly in 2029 with Ariel.

“Once LSST comes online it should detect around 10 objects like ‘Oumuamua per year. If one of these comes close enough that an interception would be possible, then ESA’s Comet Interceptor will intercept it, and prove what it is once and for all,” Seligman said.