In the 1940s, Allied pilots during the Second World War reported being hounded by fast-moving blobs, which they dubbed “foo fighters”.

Shaped like clouds, donuts, balls and spheres, and often glowing or translucent, the strange entities have fuelled conspiracy theories that Earth was being visited by advanced civilisations.

Now a paper suggests the phenomena are in fact plasmas, or ionised gases, which are drawn to the electrical charge of aircraft, spacecraft and satellites.

The team believe that plasmas in the thermosphere – 66 to 372 miles high – may descend into the lower atmosphere, and account for reports by pilots.

Co-author Dr Rudolph Schild, of the Centre for Astrophysics, Harvard-Smithsonian: “These plasmas are electromagnetic entities that have a variety of shapes and sizes. They have repeatedly approached spacecraft and the space shuttles and are attracted to electromagnetic activity including thunderstorms.

“They have been filmed from space, descending into the lower atmosphere and appear to be attracted to airplanes, fighter jets, nuclear power plants, and “hot spots” of radiation, such as Hiroshima, which was destroyed by an atomic bomb.

“Based on video, photographic and computerised analysis, including reports by military officers and astronauts, we believe these plasmas account for at least some of the numerous reports of UFOs and Unidentified Aerial Phenomenon over the last several thousand years including the ‘foo fighters’ observed by German, Japanese and Allied pilots during WWII.”

Commenting on the research, Daniel Mitchard, a lecturer at Cardiff University’s School of Engineering said: “It’s not surprising that previously unknown charge-based phenomena exist at this altitude, and that they exhibit behaviour that we don’t yet fully understand.

“It’s also likely that they will be attracted to, or repelled from, satellites and the Space Shuttle, which can build up static charges of their own.

“Even at ground level, glowing balls from thunderstorms that behave strangely are occasionally reported, often called Ball Lightning, and no one knows what these are either - they may be the same as ‘foo fighters’. It’s definitely interesting research.”

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