Tag Archives: Pluto

Arrokoth (originally named Ultima Thule) – The First Visit to a Kuiper Belt Object at the Fringe of Our Solar System

Peter Lobner, updated 24 Jan and 12 Nov 2019

The National Aeronautics and Space Administration’s (NASA) durable New Horizon spacecraft made its close flyby of Pluto on 14 July 2015, passing 7,800 mi (12,500 km) above the surface of that dwarf planet and returning a remarkable trove of photos and data.  Since then, the spacecraft has been continuing its journey out of our solar system and now is flying through the Kuiper Belt, which is a very large, diffuse region beyond the orbit of Neptune containing millions of small bodies in distant orbits around the Sun.  These Kuiper Belt Objects (KBOs) are believed to be “leftovers” (i.e., they never coalesced into planets) from the formation of the early solar system.  You can read more about the Kuiper Belt on the NASA website here:


On 28 August 2015, NASA announced that it had selected the next destination for New Horizons after the Pluto flyby: a small KBO designated 2014 MU69, originally named Ultima Thule, about 1 billion miles (1.6 billion km) beyond Pluto.  The spacecraft’s trajectory from Earth to Ultima Thule is shown in the following NASA diagram.

Source: NASA, Johns Hopkins University Applied Physics Lab, Southwest Research Institute

On 1 January 2019, the New Horizons spacecraft made a close flyby of 2014 MU69, at a range of 2,200 miles (3,500 km) and a relative speed of 14 kilometers per second (31,317 mph). At a distance of 4.1 billion miles (6.6 billion km) from the Earth, radio signals took 6 hours and 6 minutes traveling at the speed of light to traverse the distance between the spacecraft and Earth during the encounter. On 1 January 2019, NASA released the following blurry image, which was taken at long range.

Credits: NASA/JHUAPL/SwRI; sketch courtesy of James Tuttle Keane

NASA reported: “At left is a composite of two images taken by New Horizons’ high-resolution Long-Range Reconnaissance Imager (LORRI), which provides the best indication of Ultima Thule’s size and shape so far. Preliminary measurements of this Kuiper Belt object suggest it is approximately 20 miles long by 10 miles wide (32 kilometers by 16 kilometers). An artist’s impression at right illustrates one possible appearance of Ultima Thule, based on the actual image at left. The direction of Ultima’s spin axis is indicated by the arrows. “

In the weeks following the flyby, New Horizons will be downloading all of the higher-resolution photos and data acquired during its close encounter with 2014 MU69 and we’ll be getting a much more detailed understanding of this KBO. 

It appears that NASA has the opportunity to target one or more additional KBOs for future New Horizons flybys in the 2020s.  The spacecraft’s electric power source, a plutonium (Pu-238)-fueled radioisotope thermoelectric generator (RTG), is capable of providing power well into the 2030s, albeit at gradually reducing power levels.  In addition, the spacecraft has significant hydrazine fuel remaining for course correction and attitude control en route to a future KBO flyby.

On 2 January 2019, NASA released the following photo taken on the inbound leg of the flyby, still 18,000 miles (28,000 km) from 2014 MU69.

Source: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

You’ll find more information on NASA’s New Horizons mission here:


24 January 2019 Update:  Latest photo shows 2014 MU69 surface to be unusually smooth

Today, NASA released the following photo of 2014 MU69, taken at a distance of 4,200 miles (6,700 kilometers) on 1 January 2019, just seven minutes before closest approach.  Principal Investigator Alan Stern, of the Southwest Research Institute, reported, “Over the next month there will be better color and better resolution images that we hope will help unravel the many mysteries of Ultima Thule.”

Source: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

12 November 2019:  2014 MU69 renamed

NASA announced that 2014 MU69 was formally renamed “Arrokoth”, which NASA says “means ‘sky’ in the language of the Powhatan people, a Native American tribe indigenous to Maryland. The state is home to New Horizons mission control at the Johns Hopkins University Applied Physics Laboratory in Laurel.”  Here’s a colorized view of Arrokoth. 

Source: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

NASA Announces New Findings on the Behaviors of Pluto and Its Five Known Moons

Peter Lobner

On 28 May 2015, NASA presented surprising information, derived from observations by the Hubble Space Telescope, on the behaviors of Pluto and it’s five known moons: Charon, Hydra, Nix, Kerberos, and Styx. Details of the study were reported in the paper, “Resonant Interactions and Chaotic Rotation of Pluto’s Small Moons,” by Douglas Hamilton and Mark Showalter, in the 3 June 2015 issue of Nature.

An artist’s conception of the relative sizes and shapes of Pluto’s known moons is shown in the following figure:

image Source: NASA

The largest moon, Charon, and Pluto form a binary system that orbits a point between the two, as shown in the following figure, in which Pluto’s orbit is shown in red and Charon’s orbit is shown in green.

image Source: NASA

As described in my 14 March 2015 post, this binary system behavior also was observed from the New Horizons spacecraft, which is approaching Pluto for a flyby on 14 July 2015.

The Pluto-Charon binary system creates an irregular, rotating, dumbbell-shaped gravitational field that acts on the other moons orbiting the binary pair, resulting in chaotic (unpredictable in the long-term) orbits of the outer moons. The behaviors of Hydra and Nix are further complicated by their non-spherical shapes and tumbling orbital flight. Nonetheless, it appears that the orbits of Hydra, Nix and Styx are synchronized with each other in a 3-body resonance.

You can read more details on the 28 May NASA briefing at the following link:


The New Horizons Mission to Pluto

Peter Lobner

The New Horizons spacecraft is scheduled for a flyby of Pluto and its five known moons on July 14, 2015.  Launched in January 2006, New Horizons has gone through 18 “hibernation” cycles enroute to Pluto.  It came out of its last hibernation cycle on December 6, 2014.  New Horizons electrical systems are powered by a radioisotope thermoelectric generator (RTG) that produces electricity from the heat of decaying Plutonium 238.  Propulsion is by means of hydrazine thrusters.

plutonewhorizons-nasa New Horizons spacecraft. Source: NASA
You can find details on the design of the New Horizons spacecraft at the following link:
New Horizons trajectory from Earth included a gravity-assist from Jupiter.
trajectoryImage Source: NASA
Here’s a New Horizons photo of Jupiter during it’s 2007 flyby:
jupiter-io Source: NASA
Pluto and moon Charon viewed from New Horizons in January 2015:
Source: NASA

You can see an interesting NASA time-lapse “video” sequence of  Charon circling Pluto at the following link:


As noted in that article, Charon’s mass is roughly a tenth of Pluto’s, which gives it enough gravitational pull to have a noticeable effect on Pluto’s position.

You can follow details on the New Horizons mission on the following NASA website: 


 After the Pluto encounter, New Horizons will continue on to visit one or more objects in the Kuiper Belt, which circles our solar system beyond the orbit of Pluto.  The Hubble space telescope has been used to search for potential Kuiper Belt Objects (KBOs).