Because of the absence of gravity, fuels burning in space behave very differently than they do on Earth. In this image, a 3-millimeter diameter droplet of heptane fuel burns in microgravity, producing soot. This colorized grayscale image is a composite of the individual video frames of the backlit fuel droplet. The bright yellow structure in the middle is the path of the droplet, which becomes smaller as it burns. Initial soot structures (in green) tend to form near the liquid fuel. These come together into larger and larger particles which ultimately spiral out of the flame zone in long, twisting streamers.