Europe's most active volcano, Mount Etna, put on a spectacular show this weekend. It exhaled a series of near-perfect circles, resembling smoke rings or even a fleet of giant spaceships peacefully drifting across the sky.
Scientists have a more down-to-earth explanation for this phenomenon. These are "volcanic vortex rings," formed by the rapid release of gas and vapor from a new crater on Mount Etna.
"The rings look pretty much like the 'smoke rings' produced by an able smoker," Boris Behncke, a volcanologist at the Italian National Institute of Geophysics and Volcanology's Etna observatory, told The Washington Post.
The unusual rings, according to Mr Behncke, are a result of gassy magma bubbling up beneath a cylindrical opening that formed in a new crater on Mount Etna last week.
"Imagine a very narrow, cylindrical conduit, within which, at a certain depth, there is magma," Mr Behncke said. "Every so often, a bubble forms at the surface of the magma, bursts, and sends a slug of gas at high speed through that conduit."
As gas bubbles rise through the narrow, circular vent, they're squeezed into its shape, creating ring-shaped puffs.
"You won't get rings from a more irregular shape of the vent," he told the media outlet.
These gas rings are about 80% water vapour, with the rest being mostly sulfur dioxide and carbon dioxide. Mr Behncke explains that it's the water vapour that makes them appear white and puff out like smoke rings.
The composition of these gas rings is roughly 80% water vapour, with the remaining 20% dominated by sulfur dioxide and carbon dioxide. According to Mr Behncke, it's the water vapour that condenses in the cooler air, giving the rings their white, smoky appearance.
According to Mr Behncke, the rings are not particularly rare phenomena. Etna is "the most prolific volcano on this planet in terms of vapour rings," he said.
