A New Jovian Mini-Moon

Discovered with DECam on the CTIO Blanco telescope, the diminutive moon S/2017 J1, only a mile across, takes 2 years to complete an orbit around Jupiter. Its retrograde orbit — in the direction opposite to Jupiter’s spin — tells us that the moon originated elsewhere and was captured by Jupiter. The inset shows the discovery images taken by astronomers Scott Sheppard and Chad Trujillo. The discovery brings to 69 the total number of Jovian moons known.