New Horizons Approaching Historic Flyby of Ultima Thule, 4 Billion Miles Away

Artist’s conception of New Horizons at Ultima Thule. Image Credit: NASA/JHUAPL/SwRI Illustration/Steve Gribben

Excitement is building again for New Horizons team members and the public alike, as the spacecraft which previously visited Pluto is now only 21 days away from its next historic flyby, some 4 billion miles from Earth and one billion miles beyond Pluto itself.

The target is a small rocky body, a Kuiper Belt Object (KBO) named ‘Ultima Thule’, and New Horizons is now closing in at a speed of almost one million miles per day, aiming for a New Years Eve flyby just after 12:33am EST on Jan. 1, 2019.

The encounter will mark a historic milestone for the most distant object ever visited by a spacecraft in our Solar System.

Ultima Thule (aka 2014 MU69) will also be the first object visited by New Horizons since its epic flyby of Pluto in July 2015. It will be exciting to see a new world up-close again for the first time ever. Ultima Thule is a very small rocky body, much smaller than Pluto – more like an asteroid, at only about 16 miles (25 kilometers) in diameter. But it will provide valuable information as to how these KBOs – left over from the formation of the Solar System – originated.

As New Horizons Principal Investigator Alan Stern tweeted recently:

Ultima Thule being so small and dim means that conducting a flyby of it is more difficult than Pluto.

“This flyby is a lot harder than Pluto,” Stern said. “Ultima is tiny, and faint, much harder to navigate on… Another difficulty, or challenge, really, is that we’re farther away, and that means communication times are longer. Bit rates are lower.”

“It’s a one-shot, ‘get it right or go home’ deal, because there’s no U-turn to go back and have a re-do… You have to plan every chess move with the spacecraft more carefully.”

Last August, New Horizons made its first visual detection of Ultima Thule from more than 100 million miles away.

“The image field is extremely rich with background stars, which makes it difficult to detect faint objects,” said Hal Weaver, New Horizons project scientist and LORRI principal investigator from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. “It really is like finding a needle in a haystack. In these first images, Ultima appears only as a bump on the side of a background star that’s roughly 17 times brighter, but Ultima will be getting brighter – and easier to see – as the spacecraft gets closer.”

Composite image of Ultima Thule taken by New Horizons on Dec. 1, 2018. UT still just looks like a bright dot, but that will soon change. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

From that distance, Ultima Thule still looked like just a dot of light among the background stars, but soon now we will have close-up images of this remote little world.

The images were used to help the New Horizons team refine the spacecraft’s trajectory toward its target.

“Our team worked hard to determine if Ultima was detected by LORRI at such a great distance, and the result is a clear yes,” said Stern. “We now have Ultima in our sights from much farther out than once thought possible. We are on Ultima’s doorstep, and an amazing exploration awaits!”

When New Horizons reaches Ultima Thule, it will be about an incredible 1 billion miles beyond Pluto. Ultima Thule is 4.1 billion miles (6.6 billion kilometers) from Earth.

The spacecraft will also pass closer to Ultima Thule than it did Pluto, at a distance of 2,200 miles – less than a third of the distance of the Pluto flyby. The images it sends back will be even higher resolution than those taken at Pluto. According to Stern:

“We will obtain geologic mapping resolutions as high as 35 meters (110 feet) per pixel using LORRI. By comparison, our highest resolution Pluto mapping was about 80 meters (260 feet) per pixel.”

Timeline of closest approach to Ultima Thule. Image Credit: NASA/JHU-APL/SWRI
Illustration of the “big picture” view of New Horizon’s trajectory from Earth to Pluto, Ultima Thule and beyond. Image Credit: NASA/JHU-APL/SWRI

On October 3, New Horizons performed a short engine burn to further refine the location and timing of the flyby.

“Thanks to this maneuver, we’re right down the middle of the pike and on time for the farthest exploration of worlds in history – more than a billion miles beyond Pluto,” said Stern. “It almost sounds like science fiction, but it’s not. Go New Horizons!”

“The recent navigation images have helped us confirm that Ultima is within about 300 miles [500 kilometers] of its expected position, which is exceptionally good,” said Fred Pelletier, New Horizons navigation team chief, of KinetX Aerospace, Inc. “We’re excited for the flyby.”

The Kuiper Belt is a remote region of the outer Solar System which Pluto and Ultima Thule are part of. New Horizons is the first mission to ever explore this lonely expanse.

The New Horizons team also recently finished a 3-day rehearsal from the big event, from September 6-8.

“This was our science team’s final exam,” said Stern. “And they passed it with flying colors – meaning we’re ready for the Ultima flyby coming almost exactly 100 days from now!”

Overview of the Ultima Thule flyby mission. Image Credit: NASA/JHU-APL/SWRI
What will Ultima Thule look like? Image Credit: NASA/JHU-APL/SWRI

“New Horizons is already conducting humankind’s first-ever close flyby of a small Kuiper Belt object, an incredible feat by itself,” said Weaver. “But If the real Ultima is half as cool as the one we simulated in this test, we’re in for an even more amazing start to 2019!”

Few specific details about Ultima Thule are know at this point, but that will soon change. Some data obtained already suggests that it may be two smaller bodies stuck together, like a binary asteroid, rather than just one object.

Back in 2015, New Horizons provided the first close-up views of Pluto and its moons, revealing worlds more geologically diverse than previously thought possible, with tall water ice mountains, canyons, nitrogen ice glaciers and plains, possible ice volcanoes and huge ice spikes resembling earthly penitentes.

So what comes after Ultima Thule? There are still additional KBOs that New Horizons could potentially rendezvous with.

“We’re going to look for another flyby target, and we’re going to continue to observe Kuiper Belt objects with the telescopes on board,” Stern said. “If NASA approves that, there will be a third act.”

But even if that doesn’t happen, New Horizons has already transformed our view of the worlds in the Kuiper Belt and will have shown us views of the most distant object ever visited by a spacecraft from Earth – an unparalleled achievement.

See also Alan Stern’s new article about Ultima Thule on Sky & Telescope.

You can follow New Horizons’ current position here (last updated today, December 10). More information about New Horizons is available on the mission website (new design!).

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