Amalthea is Jupiter’s largest non-Galilean regular satellite. It is also the largest of Jupiter’s inner moons and the fifth-largest Jovian moon overall, after Io, Europa, Ganymede, and Callisto.
Edward Emerson Barnard discovered Amalthea on 9 September 1892 at Lick Observatory. It was the first new moon of Jupiter found since Galileo’s observations of the four Galilean moons in 1610, and it was the last planetary satellite discovered by direct visual observation rather than photography.
Amalthea is irregularly shaped, reddish, and heavily cratered. Its dimensions are about 252 × 146 × 126 kilometers, but its low density suggests a porous, ice-rich body. It orbits Jupiter roughly 181,000 kilometers away and lies near the outer edge of the Amalthea Gossamer Ring, whose dust probably comes from impacts on the moon.
A common mix-up is confusing “largest non-Galilean” with “largest regular satellite” in a broader classification. In the usual Jovian-moon context, Amalthea is the accepted answer; Thebe, Adrastea, and Metis are all smaller inner moons.