Credit: NASA/JPL-Caltech/DLR/NAU

With the help of NASA's Spitzer Space Telescope, astronomers have discovered that what was thought to be a large asteroid called Don Quixote is in fact a comet.

Don Quixote's coma and tail -- features of comets -- as revealed in infrared light by Spitzer. The coma appears as a faint glow around the center of the body, caused by dust and gas. The tail points towards the right-hand side of Don Quixote, into the direction opposite of the sun.