New Year rendezvous in the Kuiper Belt

NASA’s New Horizons spacecraft on target to reach Ultima Thule

29 December 2018

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  • Nahvorbeiflug von New Horizons an Ultima Thule am 1. Januar 2019
    New Horizons’ close flyby of Ultima Thule on 1 January 2019

    In 61 years of space exploration, no spacecraft has examined an object further away from the Earth and Sun at close quarters: on 1 January 2019, NASA’s New Horizons spacecraft will fly past the approximately 30-kilometre trans-Neptunian object, 2014 MU69, which is 6.5 billion kilometres from the Sun. The body has been given the provisional name Ultima Thule by the project scientists. Ultima Thule is an object in the Kuiper-Edgeworth belt. New Horizons – in front of the Sun (upper right corner) in this artist’s impression – will pass Ultima Thule at a distance of just 3500 kilometres. It takes a signal from New Horizons over six hours to reach Earth (one way).

  • Der Weg von New Horizons in den Kuipergürtel zu Ultima Thule
    The route from New Horizons to Ultima Thule

    New Horizons is a space probe from NASA's New Frontiers programme. The main goal is the investigation of the dwarf planet Pluto up close. Launched on 19 January 2006, it reached its destination on 14 July 2015. The images from the Pluto-Charon system taken from a distance of 12,500 kilometres were a sensation. Since the New Horizons spacecraft is not an orbiter, after the encounter with Pluto-Charon there was an opportunity to target another target in the Kuiper Belt. The Kuiper Belt is a region that extends beyond Neptune's orbit to 18 billion kilometres from the Sun. Here, there are thousands of 'Kuiper-Belt Objects' (KBOs) at extremely low temperatures, from primitive bodies only a few kilometres in size to the dimensions of dwarf planets. And it is there that New Horizons is visiting 2014MU69, which is currently known as 'Ultima Thule'.

  • Vorstellung von Ultima Thule als Doppelkörper
    The idea of Ultima Thule being two bodies

    The exact shape of Ultima Thule, which NASA’s New Horizons spacecraft will fly past on 1 January at a distance of 3500 kilometres, is not yet known. Based on light curve analysis during a stellar occultation in July 2017, scientists assume that Ultima Thule extends for 30 kilometres, has an irregular shape and presumably consists of two bodies. It could therefore be a so-called contact binary with possibly only extremely loose cohesion – similar to the comet, 67P/Churyumov-Gerasimenko.

  • Vorstellung von Ultima Thule als Einzelkörper
    Ultima Thule as a single body

    Artist’s impression of the trans-Neptunian object (486958) 2014 MU69, or Ultima Thule, as a 30-kilometre coherent body. Based on the light curves obtained from ground-based telescopes and the SOFIA airborne observatory, it is not entirely clear whether the target object of NASA’s New Horizons spacecraft for 1 January 2019 has one or possibly two bodies, which are either totally separate or weakly joined.

  • New Horizons
    New Horizons

    NASA's New Horizons spacecraft is 0.7 metres tall, 2.1 metres long, 2.7 metres at its widest and weighs 478 kilograms. With an initial speed of 16 kilometres per second, it was the fastest spacecraft to leave Earth. The science payload has a mass of 31 kilograms that consume 30 watts. There are seven experiments: Alice: Ultraviolet imaging spectrometer; analyses composition and structure of Pluto's atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects; LORRI Long Range Reconnaissance Imager (20.8 cm Telescopic camera; obtains encounter data at long distances); PEPSSI - Pluto Energetic Particle Spectrometer Science Investigation (Energetic particle spectrometer; investigats the immediate environment of the body); Ralph - Visible and infrared imager/spectrometer (provides colour, composition and thermal maps); REX - Radio Science EXperiment (Measures atmospheric composition and temperature; passive radiometer); SDC - Student Dust Counter (measures the space dust); SWAP - Solar Wind Around Pluto (Measures interaction solar wind and magnetic field).

  • On 1 January 2019, NASA’s New Horizons spacecraft will encounter the Kuiper Belt object nicknamed Ultima Thule.
  • The appearance and composition of this object are as yet unknown.
  • On board the spacecraft is the REX radio experiment funded by the DLR Space Administration.
  • Focus: exploration, space travel, planetary research

A very special encounter is set to take place in the Kuiper Belt, six and a half billion kilometres from Earth, right at the beginning of the New Year. NASA’s New Horizons spacecraft will visit object 2014 MU69, better known as Ultima Thule. At 06:33 CET, New Horizons will fly past Ultima Thule and use its measuring equipment to examine the object from a distance of just 3500 kilometres. New Horizons was launched to space approximately 13 years ago to investigate the dwarf planet Pluto. This is the first close-up exploration of a body beyond Pluto.

During the relatively brief Ultima Thule flyby phase, at a speed of 14 kilometres per second, seven scientific experiments will record images, spectra and physical measurement values. On board the spacecraft are two plasma instruments (PEPSSI and SWAP), one dust detector (Venetia), a radio experiment (REX) and three optical devices: the UV spectrometer Alice and the LORRI and Ralph high-resolution camera systems. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration has supported Martin Pätzold’s participation in the REX experiment with funds provided by the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi). REX will use radio waves to determine the thermal radiation and mass of Ultima Thule. It is the only instrument on board New Horizons that involves a contribution by German planetary researchers. During the flyby, Pätzold, Deputy Director of the Rhenish Institute for Environmental Research at the University of Cologne (EURAD), together with Michael Bird will perform two measuring procedures. REX will determine the surface temperature, mass and density of Ultima Thule. These values will provide an indication of the object’s internal composition and how it formed over four and a half billion years ago at the edge of the solar nebula.

First impression of the unknown object

In the run-up to the forthcoming rendezvous, planetary researchers managed to gain a ‘glimpse’ of Ultima Thule. In mid-August 2018, the Long Range Reconnaissance Imager (LORRI) spotted the relatively small object from a distance of 172 million kilometres as a tiny pinprick of light surrounded by a multitude of background stars. Although no surface structures were discernible from this distance, the position confirmed that New Horizons was on the right course to pass Ultima Thule as predicted on the morning of 1 January 2019 – a premiere for all solar system researchers. By the end of New Year Day, when the first images arrive, scientists are likely to know whether it is a round or oblong object, whether there are one or more objects, and what the surface is like. Researchers assume that Ultima Thule will be between 20 and 30 kilometres in size.

Ultima Thule – mystery at the edge of the Solar System

Ultima Thule was discovered on 26 June 2014 with the Hubble Space Telescope during a search for possible objects in the Kuiper Belt that appeared to be potential targets for NASA’s New Horizons spacecraft during the period following its flyby of the dwarf planet Pluto and its moon Charon. Ultima Thule orbits the Sun at distances of between 6.4 and almost seven billion kilometres.

The new object was initially labelled 1110113Y. In May 2015, when its orbit was determined with sufficient accuracy, it was given the official designation 2014 MU69. In March 2018, the New Horizons team selected the nickname, Ultima Thule, from the suggestions submitted. According to Celtic-German legend Ultima Thule represents a fictional, far-flung place in the far north, beyond the mythical island of Thule at the end of the world – a symbolic name for the exploration of the unknown. Ultima Thule will only be given its definitive name after the coming flyby, once it is clear what the object actually looks like.

In 2017 and 2018, the observations of stellar occultation by Ultima Thule indicated that the object may consist of two bodies orbiting each other. The DLR- and NASA- operated SOFIA airborne observatory played a decisive role in these observations. The upcoming observations will therefore be extremely exciting and enlightening for the planetary researchers.

The Kuiper Belt

The Kuiper Belt, sometimes also referred to as the Kuiper-Edgeworth Belt, is the cosmic home of Ultima Thule. It is a donut-shaped region of icy, sometimes extremely primitive, bodies ranging from a few kilometres to several thousand kilometres in diameter, such as the dwarf planets Pluto, Eris, Makemake and Haumea. The Kuiper Belt is immediately adjacent to Neptune and probably extends to a distance of 18 billion kilometres from the Sun. It is also the source of most short-period comets. Together, all the objects in the Kuiper Belt have only a fraction of the Earth’s mass.

  • Ultima Thule in numbers


    Discovery 26 June 2014
    BDesignation (486958) 2014 MU69, Ultima Thule; 110113Y
    Minor planet number 486958
    Orbital parameters:  
    Aphelion distance 6983 million kilometres
    Perihelion distance 6355 million kilometres
    Semi-major axis 6667 million kilometres
    Orbital inclination 2.45 degrees
    Orbital eccentricity 0.036
    Orbital period 297 years
    Physical data  
    Mean diameter 25 kilometres (min.) - 45 kilometres (max.)
    Apparent magnitude 26.8 mag
    Absolute magnitude 11.1 mag


  • The New Horizons spacecraft

    New Horizons was launched from Cape Canaveral (Florida) on 19 January 2006 with the aim of flying to the dwarf planet Pluto and continuing through the Kuiper Belt. On 28 February 2007, this almost 500-kilogram spacecraft was boosted to its final cruising speed during a close-up flyby of the giant planet Jupiter. It then travelled away from the Sun at 83,600 kilometres per hour, flying past Pluto and Charon on 14 July 2015 at a speed of 50,400 kilometres per hour. The images revealed the entirely unexpected, astonishing surface structures of the dwarf planet Pluto and its moon Charon. Its forthcoming flyby of 2014 MU69 is also expected to deliver surprising results.

Last modified:
29/12/2018 10:13:07



Ulrich Köhler
German Aerospace Center (DLR)

Tel.: +49 30 67055-215

Fax: +49 30 67055-303
Dr Manfred Gaida
German Aerospace Center (DLR)

Space Administration

Tel.: +49 228 447-417

Fax: +49 228 447-745
Dr Martin Pätzold
Rhenish Institute for Environmental Research at the University of Cologne (EURAD)

Planetary Science

Tel.: +49 170 2947-318