Ultima Thule is the single farthest object in the solar system and for the first time in spacefaring history, humans are exploring it in great detail. Since NASA first approached the oddly-shaped space rock on New Year’s Day this year, New Horizons has collected a treasure trove of information. But the latest batch of Ultima Thule observations may just prove to be the most surprising snapshots yet. A sequence of 14 close-up images taken when New Horizons was 5,494 miles (8,862 km) past Ultima Thule has completely changed the way scientists think the rock is shaped.
Until now, Ultima Thule was thought to be oddly snowman-like – built from two spherical rocks, where one is larger than the other.
NASA’s new observations, however, reveal a flatter and more pancake-like space rock.
Alan Stern, New Horizons principal investigator, said: “This is really is an incredible image sequence, taken by a spacecraft exploring a small world four billion miles away from Earth.
“Nothing quite like this has ever been captured in imagery.”
NASA has now confirmed Ultima Thule resembles two pancakes or a “dented walnut” more than it does a snowman.
But there is still some uncertainty about the true shape of the object because vast swathes if its surface are hidden away from the Sun’s light.
Instead, astronomers had to approximate Ultima Thule’s shape by charting out the parts of the rock which blocked out the starlit background behind it as the pictures were taken.
This allowed NASA to create an updated outline for the rock and create a sharpened and illuminated crescent around its edge.
Dr Stern said: “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.
“It would be closer to reality to say Ultima Thule’s shape is flatter, like a pancake.
“But importantly, the new images are creating scientific puzzles about how such an object could even be formed.
“We’ve never seen anything like this orbiting the Sun.”
Ultima Thule, or more specifically Kuiper Belt Object 2014 MU69, is a so-called trans-Neptunian binary rock in the Kuiper Belt, a field of asteroids in the outer reaches of the solar system.
The object is made up of two separate bodies, about 12 miles (19km) and nine miles (14km) long respectively.
The two rocks are dubbed Ultima and Thule, giving the space rock its conjoined name.
Ultima Thule was first discovered by astronomer Marc Buie in June 2014 with the aid of the Hubble Space Telescope.