New Photos Reveal Ultima Thule Is a Pancake Stuck to a Dented Walnut

When New Horizons beamed back its first images of Ultima Thule, the Kuiper Belt Object (KBO) and most distant object ever explored by humans, scientists and the press excitedly noted that it appeared to be an ancient contact binary composed of two spherical shapes compressed at their point of mutual contact. It looked, to many eyes, like a two-lobed snowman. But this image (shown above) isn’t as complete a picture of the shape as we thought it was. It’s the best photo of Ultima Thule available, but it appears to have captured the contact binary face-on, rather than from the edge.

New Horizons has been rocketing away from Ultima Thule since New Year’s Day, but the data rate on the spacecraft is so low, we’re still receiving telemetry from its initial encounters. Here’s what NASA writes:

The first close-up images of Ultima Thule – with its two distinct and, apparently, spherical segments – had observers calling it a “snowman.” However, more analysis of approach images and these new departure images have changed that view, in part by revealing an outline of the portion of the KBO that was not illuminated by the Sun, but could be “traced out” as it blocked the view to background stars.

Stringing 14 of these images into a short departure movie, New Horizons scientists can confirm that the two sections (or “lobes”) of Ultima Thule are not spherical. The larger lobe, nicknamed “Ultima,” more closely resembles a giant pancake and the smaller lobe, nicknamed “Thule,” is shaped like a dented walnut.

Here’s what that looks like, according to NASA:

There are video clips available on NASA’s site. According to principal investigator Alan Stern of the Southwest Research Institute, “We’ve never seen something like this orbiting the Sun.”

Part of what makes Ultima Thule so interesting is that it’s a veritable time capsule from the oldest era in our Solar System. While KBOs were once far more common than they are now, the most distant areas of our planetary system probably never contained as much bulk material as the areas closer to the Sun. We’ve talked before about how dwarf planets, like Ceres, are believed to represent a critical stage in planetary evolution as the objects that would become the inner and outer planets “bulked up” from asteroid rubble piles to planetesimals, to dwarf planets, to planets. Objects like Ultima Thule represent an even earlier stage in that process, frozen in time for billions of years.

NASA composed this new model by observing Ultima Thule over time, watching which background stars blinked out and which did not as the asteroid rotated. Individual images were then combined to create a composite model of the overall shape. New data from the New Horizons Long Range Reconnaissance Imager (LORRI) is posted here each Friday, for those interested in seeing the raw image files before processing.