A series of images from NASA’s New Horizons spacecraft contains important scientific information about the true shape of the Kuiper Belt object Ultima Thule (2014 MU69). These images are the final views New Horizons captured of Ultima Thule as it raced away at over 31,000 mph (50,000 kmh) on January 1, 2019.
New Horizons team members created this ‘departure movie’ from 14 different images taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) instrument shortly after the spacecraft flew past Ultima Thule on January 1, 2019. The central frame of this sequence was taken at 05:42:42 GMT (12:42 a.m. EST), when New Horizons was 5,494 miles (8,862 km) beyond Ultima Thule, some 4.1 billion miles (6.6 billion km) from Earth. The object’s illuminated crescent is blurred in the individual frames because a relatively long exposure time was used during this rapid scan to boost the camera’s signal level — but the team combined and processed the images to remove the blurring and sharpen the thin crescent. This is the farthest movie of any object in our Solar System ever made by any spacecraft. The images reveal an outline of the ‘hidden’ portion of the Ultima Thule that was not illuminated by the Sun as the spacecraft zipped by, but can be ‘traced out’ because it blocked the view to background stars also in the image. Image credit: NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Institute / National Optical Astronomy Observatory.
The first close-up images of Ultima Thule — with its two distinct and, apparently, spherical segments (lobes) — had observers calling it a ‘snowman.’
However, more analysis of approach images and these new images have changed that view, in part by revealing an outline of the portion of the object that was not illuminated by the Sun, but could be ‘traced out’ as it blocked the view to background stars.
Now New Horizons team members can confirm that the two lobes of Ultima Thule are not spherical.
The larger lobe, Ultima, more closely resembles a giant pancake and the smaller lobe, Thule, is shaped like a dented walnut.
“This really is an incredible image sequence, taken by a spacecraft exploring a small world 4 billion miles away from Earth. Nothing quite like this has ever been captured in imagery,” said New Horizons principal investigator Dr. Alan Stern, a researcher at the Southwest Research Institute.
Scientists’ understanding of Ultima Thule has changed as they review additional data. The ‘old view’ in this illustration is based on images taken within a day of New Horizons’ closest approach to the object on January 1, 2019, suggesting that both of ‘Ultima’ (the larger lobe) and ‘Thule’ (the smaller lobe) were nearly perfect spheres just barely touching each other. But as more data were analyzed, including several highly evocative crescent images taken nearly 10 min after closest approach, a ‘new view’ of the object’s shape emerged. Ultima more closely resembles a ‘pancake,’ and Thule a ‘dented walnut.’ The bottom view is the team’s current best shape model for Ultima Thule, but still carries some uncertainty as an entire region was essentially hidden from view, and not illuminated by the Sun, during the New Horizons flyby. The dashed blue lines span the uncertainty in that hemisphere, which shows that Ultima Thule could be either flatter than, or not as flat as, depicted in this figure. Image credit: NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Institute.
“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 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.”
“While the very nature of a fast flyby in some ways limits how well we can determine the true shape of Ultima Thule, the new results clearly show that Ultima and Thule are much flatter than originally believed, and much flatter than expected,” said New Horizons project scientist Dr. Hal Weaver, a researcher at the Johns Hopkins Applied Physics Laboratory.
“This will undoubtedly motivate new theories of planetesimal formation in the early Solar System.”
