An image of Ultima Thule captured by New Horizons. This image was taken 28,000 km from the Kuiper Belt Object. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute


Initial data from NASA’s New Horizons probe at the Kuiper Belt Object known as Ultima Thule is already revealing some of the properties of the rocky body.

New Horizons conducted its flyby of Ultima Thule on New Year’s Day 2019.

It was the farthest flyby from Earth yet undertaken in human history, and the probe came within about 3,500 km of the object, flying past it at over 51,000 km per hour.

Ultima Thule is located in the Kuiper Belt, a collection of rocky bodies and dwarf planets on the edge of the Solar System.

End to end, the body is 31 km long and appears to consist of a large rocky sphere connected to a smaller sphere.

The larger section, named ‘Ultima’, is 19km across and the smaller ‘Thule’ section is 14km across.

Initial findings made by the science team include:

  • no evidence has been found of rings or satellites larger than 1.6km orbiting Ultima Thule
  • there is no sign of an atmosphere at the rocky body
  • the colour of Ultima Thule is similar to the colour of similar bodies in the Kuiper Belt
  • the two lobes of Ultima Thule are nearly identical in colour

The flyby is one of the last stages of the New Horizons mission, which launched on 19 January 2006 and spent six months at Pluto and its moons in summer 2015.

The mission was then extended to include a flyby of the Kuiper Belt Object named Ultima Thule.

Data transmission from New Horizons is due to resume on 10 January, and will begin a 20-month download of the spacecraft’s remaining data.

"Those of us on the science team can't wait to begin to start digging into that treasure trove," says Alan Stern of the Southwest Research Institute in Colorado, US.


"The first exploration of a small Kuiper Belt object and the most distant exploration of any world in history is now history, but almost all of the data analysis lies in the future.”


Iain Todd BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Content Editor. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.