New Horizons Team Puzzled by Lack of Light Curve from Ultima Thule

Over the past three months, NASA’s New Horizons spacecraft has been taking images to measure the brightness of its next flyby target — a Kuiper belt object nicknamed Ultima Thule (also known as 2014 MU69) — and how the brightness varies as the object rotates. Even though New Horizons team members determined in 2017 that Ultima Thule isn’t shaped like a sphere — that it is probably elongated or maybe even two objects — they haven’t seen the repeated pulsations in brightness that they’d expect from a rotating object of that shape. The periodic variation in brightness during every rotation produces what astronomers refer to as a light curve.