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Data from New Horizons as it is quickly approaching Ultima Thule has found that even though the object is expected to be oblong or even two objects it has shown absolutely no variation in light as it rotates.
Even though scientists determined in 2017 that the Kuiper Belt object 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 scientists refer to as a light curve.
“It’s really a puzzle,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute. “I call this Ultima’s first puzzle – why does it have such a tiny light curve that we can’t even detect it? I expect the detailed flyby images coming soon to give us many more mysteries, but I did not expect this, and so soon.”
They have several theories, all implausible, to explain this. It could be they are looking at the object’s pole. Or maybe a dust cloud or numerous tumbling moons surround the object and hide the light variation.
Fortunately, we shall have an answer to this mystery in less than two weeks, when New Horizons zips past.