The “air balloon” and “white line” spotted in the sky on Sunday evening were SpaceX’s Falcon 9 rocket releasing a satellite train into space, according to a University of Malta professor.

On Sunday evening several people shared photos and videos with Times of Malta and also on social media showing a "strange" white ballon-like cloud and “a white line" trailing behind it.

It was no UFO.

According to Professor Joseph Borg, Maltese sky-gazers were witnessing satellites being released into space. 

These clouds - called 'SpaceX nebula' - and a white line were spotted a couple of hours after Elon Musk's SpaceX completed another launch from the West Coast in the US: the Falcon 9 (a reusable rocket) launched more Starlink mini-satellites into space.

Starlink is a satellite internet constellation that provides global mobile broadband. 

Borg, a professor of biomedical science and director of Spaceomix - a Maltese space biotech company - explained that the white line was the satellites being released into space.

If they are seen soon after release and are still close together, they appear as a straight line. The later they are seen, he said, the more dispersed they get.

As for the cloud-like formation around these satellites, he said this might be due to several reasons, including rocket launch exhaust.

"After the launch of the Starlink satellites, the rocket’s exhaust can create a temporary cloud in space. This cloud is usually visible shortly after launch and can be illuminated by sunlight, making it visible from the ground, " he said.

The cloud could also be deployment debris. During the deployment of satellites, small particles or ice crystals might be released, forming a temporary cloud around the satellite constellation.

Another option could be satellite reflections, explained Borg.

The satellites’ solar panels and other reflective surfaces can sometimes create a visual effect that looks like a cloud, especially if the sunlight hits them at a particular angle.

The cloud could also be due to atmospheric effects. High-altitude atmospheric conditions can sometimes create optical illusions or enhance the visibility of the satellite train, making it appear cloud-like.