Small bodies · Space Codex
486958 Arrokoth
Two flattened lobes joined at a narrow neck, 36 km long, merged so gently that neither broke.
The most distant world explored up close
At a glance
Key points
New Horizons flew past on 1 January 2019.
- Visited 1 January 2019
- Two lobes merged without breaking
- About 6.6 billion km from the Sun
A fossil of planet formation
Its two lobes, Wenu and Weeyo, once orbited each other and spiralled together at walking pace. Arrokoth has barely changed in 4.5 billion years, so it preserves the conditions in which planets began to assemble.
Surface
Dark reddish-brown, with few craters and a bright collar at the neck. Methanol ice and organic material have been detected on it, but no sign of water ice.
Found just in time
Arrokoth was unknown when New Horizons launched in 2006. With the Pluto flyby approaching, the team searched for a reachable second target with Hubble and found it in June 2014: a faint point of light in a crowded star field, catalogued as 2014 MU69. Its official name came in 2019, after the flyby. The spacecraft took until late 2020 to send home all its observations, because its data rate from that distance is so low.
What the flyby settled
Simulations matched to the flyby data show the lobes formed side by side in a collapsing cloud of pebbles and touched at no more than a few metres per second. Both lobes share the same colour and make-up, so they came from the same local material rather than meeting by chance. That supports the idea that the first planetesimals grew by gentle gravitational collapse, not by violent pile-ups of smaller bodies.
Why it is red
The colour is thought to come from complex organic compounds built up over billions of years as radiation broke apart and recombined simple ices. Methanol may have formed when hydrogen combined with carbon-monoxide-rich ice in the cold outer disc. Small regional variations aside, the surface looks well mixed, as expected for a body built from one homogeneous reservoir.
Missions
- 2006–
Pluto flyby 14 Jul 2015; Arrokoth 1 Jan 2019; now studying the outer heliosphere.
Related entries
- Kuiper beltThe icy disc beyond Neptune
- PlutoDwarf planet · heart of the Kuiper belt
- New HorizonsPluto and the Kuiper belt
Sources
- McKinnon et al. 2020, solar nebula origin of Arrokoth, Science (opens in a new tab)
- NASA Science: New Horizons (opens in a new tab)
- JPL Small-Body Database: 486958 Arrokoth (opens in a new tab)
- Spencer et al. 2020, geology and geophysics of Arrokoth, Science (opens in a new tab)
- Grundy et al. 2020, colour and composition of Arrokoth, Science (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.