Free-floating planets. Computer artwork of two gas giant planets moving through space. They are not orbiting a star, but have formed independently and are called free-floating planets. Their mass is generally higher than that of Jupiter, the largest planet in our solar system, but less than that of a brown dwarf. Brown dwarfs can be considered cool stars, or large planets, that are insufficiently massive for nuclear reactions to be ignited. Cool stars and large planets can be detected by the heat (infrared radiation) they give off, which is generated as they slowly collapse by gravitational contraction. Such objects have been detected in the starbirth region known as the Orion Nebula.