At one point, the distant world Ultima Thule was assumed to be more or less a rocky ball. As New Horizons got closer, its shape was described as a bowling pin, then a snowman – and now it's changed once again. New images snapped as the probe sped away from the object show that Ultima Thule is more like a flat "pancake" stuck to a "dented walnut," leaving astronomers puzzled as to how such a shape is even possible.
Unlike previous images that were taken on approach, these new shots were snapped about 10 minutes after New Horizons made its closest pass of the object. At the central point of the 14 images, the craft was 5,494 mi (8,862 km) from Ultima Thule.
From that perspective, New Horizons was able to make out a few new details about Ultima Thule. The "crescent" of the object – the area visible from behind, as light hit it from the other side – was remarkably thin and sharp, rather than rounded. And the science team was also able to trace the shape of the darkened area by mapping how it blocked light from stars behind it.
These insights revealed that Ultima Thule is much flatter than previously thought. The team describes the larger section of the object as being shaped like a lumpy pancake, while the smaller lobe resembles a dented walnut. New Horizons, it turns out, had been approaching at exactly the right angle to only see the flat face.