New Horizons Races Toward Encounter with Ultima Thule — Most Distant World Ever Studied

James Maynard
Dec 28, 2018 · 2 min read

The New Horizons spacecraft is due to rendezvous with the most-distant object ever studied by humans, as it races toward an encounter with Ultima Thule, where it will arrive on New Year’s Day. Little is known about this distant body, discovered just four years ago.

Ultima Thule, also called 2014 MU69, resides within the Kuiper Belt, a massive collection of objects in the outer rim of our planetary system. This will mark the first time any spacecraft has studied a member of that system.

“Ultima, as the flyby target is affectionately called by the New Horizons team, is orbiting in the heart of our solar system’s Kuiper Belt, far beyond Neptune. The Kuiper Belt — a collection of icy bodies ranging in size from dwarf planets like Pluto to smaller planetesimals like Ultima Thule (pronounced “ultima toolee”) and even smaller bodies like comets — are believed to be the building blocks of planets,” the New Horizons team reported on their website.


New Horizons made history in 2015, when it became the first spacecraft to visit Pluto.

Ultima Thule is located so far from the Sun, that our parent star is only as bright as a full Moon is here on Earth. Its name is Latin for “A place beyond the known world.” Ultima was discovered in 2014, by astronomers utilizing the Hubble Space Telescope.

Astronomers know little, so far, about MU69, except that it has a diameter of around 30 kilometers (20 miles), with an irregular shape, and is dark red, reflecting just 10 percent of the meager light which strikes its surface.

Due to the nearly-circular nature of its orbit, astronomers believe that MU69 formed at its current distance from our parent star. This fact, combined with temperatures near absolute zero, make Ultima a “time capsule” showing conditions in the distant, early solar system.

Mission planners hope to fly close enough to Ultima Thule that they will be able to make out detail just 35 meters (115 feet) across. When New Horizons passed Pluto, the smallest visible details were around 75 meters (250 feet) from side-to-side.

Seen as just a tiny speck of light in the best images currently available, astronomers will soon find out if MU69 is accompanied by tiny moons, or even a ring system.

Within just 72 hours of New Horizons reaching Ultima, this distant world will be transformed in the annuals of astronomy from a tiny pinpoint of light to the first fully-explored world in the Kuiper Belt.

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