Officials in Kyiv initially suspected it was a Nasa satellite falling to Earth but the US space agency told the BBC it was still in orbit. But Rob Margetta from Nasa's office of communications told the BBC that the satellite was still in orbit at the time the flash was observed, and was due to re-enter Earth's atmosphere during the night. Ukrainian social media has been awash with theories and memes about what the flash could have been, with a popular theme being that it was caused by aliens