(CNN) Astronauts on the International Space Station are playing with fire!
They're conducting experiments on how fuel burns in microgravity.
NASA Astronaut Reid Wiseman tweeted out vines of the little fires on Thursday.
He wrote they look like "jellyfish on fire."
They're looking at how quickly fuel burns, the conditions needed for soot to form - and how mixtures of fuels evaporate before burning.
NASA says the experiments could lead to the development of safer spacecraft, and increased fuel efficiency back on earth.