One pilot, flying a Learjet over the southeastern Arizona desert, noticed an object on February 24 and immediately reported it to air traffic control in Albuquerque, New Mexico.
"I don't know what it was. It wasn't an airplane… the path was going in the opposite direction," the pilot said.
Air traffic controllers then asked a nearby American Airlines passenger jet headed from San Francisco to Dallas to notify them if any objects pass over the aircraft.
Moments later, the AA pilot saw the object in question.
"Something just passed over us, like a, don't know what it was, but it was at least two, three thousand feet above us," he said. "Yeah it passed right over the top of us."
"Was it a Google balloon?" an air-traffic controller asked.
"Doubtful," the pilot replied.
Two months later and it is still unknown what the mysterious object really was.
"We don't have any comment beyond what you hear," Federal Aviation Administration spokesperson Lynn Lunsford recently told the NBC station in Albuquerque. "Other than the brief conversation between two aircraft, the controller was unable to verify that any other aircraft was in the area."
At the very least, it probably wasn't a privately operated drone, since the object was spotted above 40,000 feet, which is higher than the range of typical consumer drones.
Although the sightings were reported close to Davis-Monthan Air Force Base and about 100 miles from Luke Air Force Base, Lunsford explained that air traffic controllers are usually notified of military aircraft flying in the area.
"We have a close working relationship with a number of other agencies and safely handle military aircraft and civilian aircraft of all types in that area every day, including high-altitude weather balloons," Lunsford said, the Huffington Post reported.