Dysnomia is the only known moon of the Kuiper Belt dwarf planet Eris. It’s the second-largest known moon of a dwarf planet, after Pluto’s moon Charon. It is named Dysnomia after the daughter of the Greek goddess Eris. The Ancient Greek word Δυσνομία means anarchy/lawlessness.

Eris is the bright object in the center of the image. Dysnomia is the smaller dot at about 8 o’clock.

Image Credit: NASA

Eris and Dysnomia

This image was taken by the Hubble Space Telescope of the dwarf planet Eris. Its moon Dysnomia can be seen near by at roughly the eight-o’clock position. Eris is a the ninth largest known body orbiting the sun. It’s orbit is out in the region past the planet Neptune known as the Kuiper belt; its distance from the Sun is almost 97X that of the Earth or roughly 3X that of Pluto. With the exception of some comets, Eris and Dysnomia are currently the most distant known natural objects in the Solar System.

Astronomers now know that three of the four brightest Kuiper belt objects (KBOs) have satellites, but only about 10 percent of the dimmer KBOs appear to have moons. Astronomers believe that collisions between large KBOs have been frequent in the past. Impacts between bodies of the order of 1000 km across could eject large amounts of material which might form into a moon. A similar mechanism is believed to have led to the formation of Earth’s own Moon when the Earth was struck by a giant impactor early in the history of the Solar System.

Image Credit: NASA