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.

Hubble discovered Pluto’s four small moons, Nix, Hydra, Styx, and Kerberos. This is a composite of two images of the Pluto system taken by Hubble in July 2012. The blue areas are from a long exposure used to capture the tiny outer moons, but which greatly oversaturated Pluto and Charon. The dark central vertical band is from a shorter exposure designed to show Pluto and Charon more clearly. The diameters of Pluto and its moons are not to scale.

NASA, ESA, and M. Showalter (SETI Institute)

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.

Hubble observations of Pluto, mapped over spheres

Hubble’s view of Pluto provided NASA’s New Horizons mission with the best available information for planning its rendezvous with the dwarf planet.

NASA, ESA and M. Buie (Southwest Research Institute)

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's view of the first moon discovered around dwarf planet Makemake

Only about 100 miles in diameter, the tiny dot above the dwarf planet Makemake seen in this Hubble image is its orbiting moon, nicknamed MK 2.

NASA, ESA, and A. Parker and M. Buie (SwRI)

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.

Hubble Discovers Moon Orbiting Dwarf Planet Makemake Credit: NASA's Goddard Space Flight Center; Producer: Katrina Jackson

Learn More

Hubble Discovers a Fifth Moon Orbiting Pluto
The irregularly shaped moon is 6 to 15 miles across and has a 58,000-mile-diameter circular orbit around Pluto.
Hubble Finds Two Chaotically Tumbling Pluto Moons
Hubble has discovered tiny satellites orbiting Pluto and Charon.
Hubble Discovers Moon Orbiting Dwarf Planet Makemake
Hubble has uncovered a tiny moon around Makemake that is an estimated 100 miles wide.
New Hubble Maps of Pluto Show Surface Changes
Hubble's view can't see craters or mountains, if they exist on the surface, but does reveal a complex-looking and variegated world.
Hubble Finds Potential Kuiper Belt Targets for New Horizons
Hubble did a deep-sky survey to identify Kuiper Belt objects that New Horizons could potentially visit on its outbound trajectory.
Hubble Spots Icy World Beyond Pluto
Approximately half the size of Pluto, the icy world is called "Quaoar" is about 4 billion miles away, more than a billion miles farther than Pluto.