Ultima Thule (Kuiper Belt) photographed by New Horizons

The New Horizons spacecraft that was launched on 19 January 2006 and passed Pluto on 14 July 2015 continued travelling into the Kuiper Belt, and has just photographed an object named Ultima Thule (‘beyond the known world’).

This image taken by the Long-Range Reconnaissance Imager (LORRI) is the most detailed of Ultima Thule returned so far by the New Horizons spacecraft.

Image taken by the Long-Range Reconnaissance Imager (LORRI) by the New Horizons spacecraft.
Photo: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

RNZ – NASA’s New Horizons: ‘Snowman’ shape of distant Ultima Thule revealed

A new picture returned from US space agency NASA’s New Horizons spacecraft shows the little world to be two objects joined together – to give a look like a “snowman”.

The US probe’s images acquired as it approached Ultima hinted at the possibility of a double body, but the first detailed picture confirms it.

New Horizons encountered Ultima 6.5 billion km from Earth.

The event set a record for the most distant ever exploration of a Solar System object. The previous mark was also set by New Horizons when it flew past the dwarf planet Pluto in 2015.

But Ultima is a further 1.5 billion km further out.

Jeff Moore, a New Horizons co-investigator from NASA’s Ames Research Center, said the pair would have come together at very low speed, at maybe 2-3km/h. He joked that if they were cars, “you probably wouldn’t fill out the insurance form.

Ultima orbits the Sun in a region of the Solar System known as the Kuiper belt.

There are hundreds of thousands of Kuiper members like Ultima, and their frigid state almost certainly holds clues to how all planetary bodies came into being some 4.6 billion years ago.

About New Horizons and Ultima Thule:

The New Horizons team used the Hubble Space Telescope to search for the next Kuiper Belt object to fly by after Pluto. Using observations made with Hubble on June 26, 2014, the science team discovered an object that New Horizons could reach with its available fuel. The object was subsequently designated 2014 MU69, given the minor planet number 485968, and based on public votes, nicknamed “Ultima Thule”, which means “beyond the known world”.

Ultima Thule is located in the Kuiper belt in the outermost regions of the Solar System, beyond the orbit of Neptune. In the early morning of January 1st 2019 Eastern Time, NASA’s New Horizons spacecraft will fly by Ultima Thule at a distance of 3500 km (2200 miles). At this time, Ultima Thule will be at a distance of almost 6.5 billion km (4 billion miles) from the Sun, making this the most distant planetary flyby that has yet been attempted, and the first time that a Solar System object of this type has been seen close-up.

Ultima Thule measures approximately 30 km in diameter, and is irregularly shaped. In July 2017, Ultima Thule passed in front of a star as seen from Earth (a stellar occultation), allowing astronomers to determine that its shape is most likely a contact binary (two bodies that are touching) or a close binary system (two objects that are orbiting each other). An artist’s impression of Ultima Thule as a contact binary is shown in the accompanying picture.

We will only know what Ultima Thule’s surface looks like once New Horizons has sent back the first pictures after it has flown by, although based on observations of similar-sized Solar System objects, it will almost certainly display impact craters. The lighting environment at its surface is very dim, as it receives only about 0.05% of the light from the Sun that Earth does. We do know that Ultima Thule has a reddish color, probably caused by exposure of hydrocarbons to sunlight over billions of years. The flyby will also reveal whether it has any moons, or even a ring system. Ultima Thule belongs to a class of Kuiper belt objects called the “cold classicals”, which have nearly circular orbits with low inclinations to the solar plane, and which have not been perturbed since their formation perhaps 4.6 billion years ago. Ultima Thule will therefore be the most primitive planetary object yet explored, and will reveal to us what conditions were like in this distant part of the Solar System as it condensed from the solar nebula.