NASA's space ship, Nev Horizons, took this composite image of Ultima Thule around midnight EST on December 2, 2018, at a distance of 24 million kilometers. In the box on the right, the area inside the yellow box is expanded and the background stars are subtracted.
Author: NASA / JHUAPL / SvRI
Something weird happens with Ultima Thule, a distant object that NASA's Nev Horizons will fly in just 10 days.
Members of the Nev Horizons team do not think Ultima is 23 miles wide (37 kilometers) spherical; namely, the available data indicate that it is elongated or maybe even composed of two bodies that are in orbit. In this way, mission scientists were expected to see the Ultimate "curve of light": significant changes in the light that correspond to the different orientation of the object while rotating.
But this is not what showed the observations of Nev Horizons in the upcoming epic encounter of New Year's Day. Instead, Ultima's light is relatively constant, as in a spherical body. [NASA’s New Horizons Mission in Pictures]
"It's a real riddle," said Nev Horizons chief researcher Alan Stern, Southwest Research Institute in Boulder, Colorado, in a statement yesterday (December 20th). "I called this Ultimate the first riddle – why it has such a slight curve of light that we can not even detect it? I expect detailed photographs to give much more mystery soon, but I did not expect this, and so soon."
Team members came up with several possible explanations. For example, Ultimin may have turned half a rotation directly into Nev Horizons, minimizing light variations seen by the spacecraft.
It is also possible that Ultima, which is located more than 4 billion kilometers from the Sun, is surrounded by a cloud of dust that blocks light, such as a coma around the core of the comet. But the source of energy would be needed to create such a characteristic, and it is not clear what that source would be. (The sun could not make a trick from Ulmine's cold, dark environment, the mission's members said.)
"The more bizarre scenario is the one in which the Ultima is surrounded by numerous tiny, swinging months," says Anne Verbiscer, project assistant project designer Nev Horizons at the University of Virginia. "If every month has its own curve of light, then they could together create a cracked superposition of the curve of light that makes Nev Horizons look like Ultima has a small curve of light."
If this happens, that would be unprecedented. It is not known that a body of the solar system has such a satellite system, said Verbiscer.
"It's hard to say which of these ideas is right," Stern said. "Maybe it's even something we did not even think about. In any case, we'll soon get to the bottom of this puzzle – Nev Horizons will overturn Ultima and record high-resolution images on December 31 and January 1, and the first of these images will be available on Earth just a day later. When we see these high-resolution images, we will have an answer to Ultiman's disturbing, first puzzle.
Flying will be the highlight at 12:33 EST (0533 GMT) on January 1st, when Nev Horizons zoomed in at only 2,200 miles (3,540 km) of the Ultima reddish surface. It's more than three times closer than the probe reached Pluto during a historic meeting with the dwarf planet in July 2015.
Ultima, officially known as 2014 MU69, is in deep frozen state in a remote solar system for more than 4.5 billion years. Therefore, the study of the subject in close proximity should reveal the key insights on the earliest days of the Solar System, said mission team members.
Mike Valla's book on the search for alien life, "Out There" (Grand Central Publishing, 2018, illustrated by Karl Tate), is now omitted. Follow him on Twitter @ michaeldvall. follow us @ Spacedotcom or Facebook. Originally published on Space.com.