Uncovering Icy Objects in the Kuiper Belt

While probing the dwarf planet Pluto on the outskirts of our solar system, Hubble spied four previously unknown moons orbiting the icy world. The tiny moons Nix and Hydra were the first to be spotted, followed by the even tinier Kerberos and Styx. Astronomers later discovered that Nix and Hydra are rotating chaotically – that is, unpredictably – as they orbit the dwarf planet.

NASA’s New Horizons spacecraft shot past Pluto in July 2015, making detailed observations of its surprisingly varied and intriguing surface. Hubble played a critical role in helping astronomers prepare for the flyby. With frequent observations of Pluto from the early 1990s to 2010, scientists refined maps of the dwarf planet’s surface. New Horizons personnel used these maps to prepare for the spacecraft’s brief but important rendezvous with Pluto and its moons.

Peering out even farther, to the dim outer reaches of our solar system, Hubble uncovered two Kuiper Belt objects that the New Horizons spacecraft could potentially target on its continual outward journey. The New Horizons mission chose to focus on a Hubble candidate called 2014 MU69. On Jan. 1, 2019, New Horizons flew past the object – now named Arrokoth – capturing up-close imagery that revealed its double-lobed structure in fine detail, complete with fractures and pitting.

Hubble also discovered a 100-mile-wide moon in orbit around Makemake, the second-brightest icy dwarf planet in the Kuiper Belt. At 4.8 billion miles from the Sun, Makemake was discovered in 2005 using the Palomar Observatory and is approximately 870 miles across. Oddly, the moon, nicknamed MK 2, is as dark as charcoal while Makemake is as bright as fresh snow.