The United States said Monday it was investigating a "debris-generating event in outer space" after astronauts on the International Space Station were forced to prepare for a possible evacuation.

The incident came amid unconfirmed reports that Russia had carried out an anti-satellite weapon (ASAT) test—rare show-of-force demonstrations criticized by the space community because of the risk they create for crews in low Earth orbit.

"US Space Command is aware of a debris-generating event in outer space. We are actively working to characterize the debris field and will continue to ensure all space-faring nations have the information necessary to maneuver satellites if impacted," the military branch said.

"We are also in the process of working with... the State Department and NASA, concerning these reports and will provide an update in the near future.

On October 19, 2017, astronomers made the first-ever detection of an interstellar object (ISO) passing through our solar system. Designated 1I/2017 U1 ′Oumuamua, this object confounded astronomers who could not determine if it was an interstellar comet or an asteroid. After four years and many theories (including the controversial "ET solar sail" hypothesis), the astronomical community appeared to land on an explanation that satisfied all the observations.

The "nitrogen iceberg" theory stated that "Oumuamua was likely debris from a Pluto-like planet in another stellar system. In their latest study, titled "The Mass Budget Necessary to Explain "Oumuamua as a Nitrogen Iceberg," Amir Siraj and Prof. Avi Loeb (who proposed the ET solar sail hypothesis) offered an official counter-argument to this theory. According to their new paper, there is an extreme shortage of exo-Plutos in the galaxy to explain the detection of a nitrogen iceberg.

In the paper where he broached the possibility, Loeb indicated that "Oumuamua's unusual character and behavior were consistent with a solar sail.