A Russian cosmonaut on board the International Space Station has shared video of five "objects" flying over Earth.
The objects were spotted in a video intended to document the aurora seen as the space station flew over the Antarctic.
But Ivan Vagner, a cosmonaut who arrived on the floating lab in April, noted that he had seen something unexpected while taking capturing the images for the video.
In it, five "objects appear flying alongside", he said. "In the video, you will see something else, not only the aurora.
"What do you think those are? Meteors, satellites or…?" he wrote in a tweet.
The most likely explanation for the unusual video is that the five objects are Starlink satellites, part of a constellation launched by Elon Musk's private company SpaceX to provide internet to people on Earth. Those satellites fly together in orbit, and are notoriously bright as they do so – having been criticised for ruining the view of the Neowise comet and potentially interfering with astronomers' observations of the night sky.
SpaceX launched a new set of 58 Starlink satellites on Tuesday morning, and the satellites fly in particularly close formation after they are first launched. Mr Vagner did not specify when the images were taken, but he shared them roughly a day after those satellites were sent into space.
It may also be that the objects are not out in space at all, but that the bright lights are the result of glare from the ISS's windows, or dust on the camera's lens, that interfered with the images as they were being taken.
Mr Vagner noted that he was taking one image per second, and that those were then stitched into the moving video, meaning that the lights might not have actually been moving in the way they appear.
But the cosmonaut tweeted that he had passed the information on to Roscosmos, the Russian space agency, and that alongside experts it was conducting "further analysis" to be sure what the objects are.
A spokesperson for the space agency, Vladimir Ustimenko, said on television that it was too soon to know for sure what the objects might be.
"It is too early to make conclusions until our Roscosmos researchers and scientists at the Space Research Institute of the Russian Academy of Sciences tell us what they think," he said, Russian news agency TASS reported.
"It was decided to hand over those materials to experts, who will tell us what that was in their opinion."
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