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Back in early January, when scientists pulled down their first batch of data from the New Horizons spacecraft, they celebrated an odd snowman-shaped object in the outer Solar System. From this first look, it appeared as though Ultima Thule, formally named 2014 MU69, consisted of two spheres in contact with one another—a contact binary.
Now that scientists have downloaded more data from the distant spacecraft, however, our view of Ultima Thule has changed. A sequence of images captured as New Horizons moved away from the object in the Kuiper Belt at a velocity of 50,000 km/hour, taken about 10 minutes after closest approach, show a much flatter appearance.
After analyzing these new images, scientists say the larger lobe more closely resembles a large pancake, and the smaller lobe looks a bit like a walnut. The new photos reveal a dramatically different object because they were taken from a different angle than the images that were downloaded first.
“We had an impression of Ultima Thule based on the limited number of images returned in the days around the flyby, but seeing more data has significantly changed our view,” the mission's principal investigator, Alan Stern, said in a news release. “It would be closer to reality to say Ultima Thule's shape is flatter, like a pancake. But more importantly, the new images are creating scientific puzzles about how such an object could even be formed. We've never seen something like this orbiting the Sun.”
It is safe to say the new apparent shape of Ultima Thule will only increase the interest of scientists studying this object—humans have never observed an object like this in the distant Kuiper Belt so closely before.
The shape is not unprecedented. As planetary scientist Alex Parker noted on Twitter, “The larger lobe looks to have a shape similar to some of the pancake moons of Saturn, like Atlas.” However, Saturn's moons were believed to have formed near the gas giant, in the midst of its rings, rather than in deep space.
New Horizons still has much more data to send back to Earth, as its data connection over the 44.4 astronomical units (6.6 billion km) is pretty slow. More data should help to resolve some of these questions as scientists study Ultima Thule. This is important, because this object, and others like it, are thought to be “pristine planetesimals” like those that served as building blocks for larger objects in the Solar System during its early days, 4.5 billion years ago.