Images from New Horizons show that Arrokoth is a bi-lobed contact binary. This means it’s actually two objects that began orbiting each other until they somehow gently merged. The strange shape of Arrokoth, unlike any object previously visited, was the biggest surprise of the New Horizons spacecraft’s flyby.
A three-dimensional model created from images taken by the New Horizons spacecraft shows that Arrokoth is elongated and flattened. The larger lobe was found to be "lenticular," which means it's flattened and shaped like two lenses placed back to back. It has dimensions of approximately 14 × 12 × 4 miles (22 × 20 × 7 kilometers). The smaller lobe is more rounded and is approximately 9 × 9 × 6 miles (14 × 14 × 10 kilometers) in its dimensions.
The surface of Arrokoth doesn’t reflect much light, but there are bright regions, with the brightest being at the “neck” where the two lobes are joined. There are also two bright spots inside the largest crater on the surface.
In color and composition, Arrokoth resembles many other objects found in its area of the Kuiper Belt. It's very red — even redder than Pluto — and is, in fact, the reddest outer solar system object visited by spacecraft thus far.
The reddish hue is believed to result from changes in the surface materials caused by ultraviolet light and cosmic rays over billions of years. Scientists found evidence for methanol, water ice and organic molecules — a mixture very different from most icy objects explored previously by spacecraft.
No atmosphere has been detected at Arrokoth. It is too small for its gravity to hold onto an atmosphere.
Arrokoth, also known as MU69, means "“sky” in the Powhatan/Algonquian language. The name was chosen in 2019 with consent from Powhatan Tribal elders. Before its official naming, the small body was nicknamed "Ultima Thule," a mythical island in medieval literature which means "beyond the borders of the known world."
Arrokoth was discovered on June 26, 2014, by New Horizons science team member Marc Buie using NASA’s Hubble Space Telescope.
Kuiper Belt Object
Number of moons
22 miles (35 kilometers) [on long axis]
Length of day
Length of year
293 Earth years
Distance from Sun
44.6 Astronomical Units (Earth = 1)
42 Kelvin (average)