An artist's illustration of NASA's New Horizons spacecraft flying by Ultima Thule (formally known as 2014 MU69) on Jan. 1, 2019. Recent observations suggest that Ultima Thule may actually be two co-orbiting bodies.

NASA's New Horizons mission continues to check off milestones ahead of its history-making New Year's Day flyby of the distant object known as Ultima Thule.

Last month, the mission team conducted a three-day practice session for the flyby, downloading and analyzing simulated data and rehearsing how to present this information to the public and the press.

"This was our science team's final exam, and they passed it with flying colors — meaning we're ready for the Ultima flyby coming almost exactly 100 days from now!" New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, said in a statement. [Destination Pluto: NASA's New Horizons Mission in Pictures]

This science-communication exam, held from Sept. 6 through Sept. 8 at the Johns Hopkins Applied Physics Lab (APL) in Maryland, was one of the last of about two dozen "operational readiness tests" that the team has been performing in advance of the Jan. 1 flyby, mission officials said.

The simulated flyby data that the team devised depicted Ultima Thule as two objects surrounded by a thin ring of debris. The real observations could show something similar; the limited information astronomers have gathered to date suggests that Ultimate Thule, which is officially known as 2014, may consist of two bodies orbiting a common center of mass.

Astronomers think that Ultima Thule is about 23 miles (37 kilometers) wide. The distant, mysterious object lies about 1 billion miles (1.6 billion km) beyond Pluto, which was New Horizons' first flyby target. The probe zoomed within 7,800 miles (12,550 km) of the dwarf planet on July 14, 2015, beaming home stunning images of a complex world with towering water-ice mountains and vast plains of frozen nitrogen and other exotic ices.

New Horizons mission team members (from left) Kirby Runyon, Rajani Dhingra, Mallory Kinczyk and Kelsi Singer discuss the two primary objects of the simulated Ultima Thule system. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Henry Throop)

The Ultima Thule encounter is the centerpiece of New Horizons' extended mission, and the flyby should return some amazing data as well. The current plan calls for the spacecraft to zoom within just 2,200 miles (3,540 km) of Ultima Thule, which astronomers regard as a pristine relic from the solar system's planet-formation period.

"New Horizons is already conducting humankind's first-ever close flyby of a small Kuiper Belt object, an incredible feat by itself," New Horizons project scientist Hal Weaver, of APL, said in the same statement. (The Kuiper Belt is the ring of icy objects beyond Neptune's orbit.) "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!"

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