Adrastea

Adrastea, also known Jupiter XV, is an irregular-shaped satellite and the smallest of the four inner moons belonging to the outer planet of Jupiter. This satellite was discovered by David C. Jewett and G. Edward Danielson on July 8, 1979. This planet orbits on the outer edge of Jupiter's Main Ring. In fact, this planet orbits Jupiter in less time than its day. Adrastea is the first moon to have been photograph by an interplanetary spacecraft instead of telescopic photography. This spacecraft was Voyager 2.

Formation
Adrastea has a color spectrum that matches those of D-type asteroids, which are very rare in the Asteroid belt. It is believed it was thrown into deep space and pulled into Jupiter's gravitational pull and became one of its moons.

Surface
Though its visible spectrum is grey and matches that of D-type asteroids, its infrared spectrum matches that of P-type and C-type asteroids, which contain carbon-based gases, and possibly signs of water ice.

Orbit
Adrastea is the only one of three moons in the entire Solar System to orbit its primary in less time than the primary's day. The other ones being the innermost moon of Jupiter, Metis, and the largest of Mars' moons, Phobos.