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takyon writes:

New Movie Shows Ultima Thule from an Approaching New Horizons

This movie shows the propeller-like rotation of Ultima Thule in the seven hours between 20:00 UT (3 p.m. ET) on Dec. 31, 2018, and 05:01 UT (12:01 a.m.) on Jan. 1, 2019, as seen by the Long Range Reconnaissance Imager (LORRI) aboard NASA's New Horizons as the spacecraft sped toward its close encounter with the Kuiper Belt object at 05:33 UT (12:33 a.m. ET) on Jan. 1.

The images, which cover about a half of a rotation, help illustrate the solution to Ultima Thule's apparent lack of brightness variations:

The brief video also shows why New Horizons didn't detect any brightness variations from Ultima Thule during the approach phase, a surprising development that initially puzzled the mission team. The lack of such a "light curve" is expected for spherical objects, which don't shift from a viewer's perspective as they rotate, but early data indicated that the 21-mile-long (34 km) Ultima Thule was highly elongated.

As we can now see, it was all about New Horizons' orientation to Ultima Thule. The object's pole of rotation was pointing directly at the approaching spacecraft, so New Horizons didn't see any appreciable changes in the light bouncing off Ultima Thule.

Previously: New Horizons Survives Flyby, Begins Sending Back Data
New Images Reveal Structure, Color, and Features of 2014 MU69 (Ultima Thule)

Original Submission