Author: Lisa Grossman / Source: Science News
Ultima Thule has a new mug shot.
The closest-yet image of the ancient Kuiper Belt object, captured as the New Horizons spacecraft flew by January 1, shows a relatively smooth face unmarred by impact craters.
“The thing is just not covered in craters,” says planetary scientist Kelsi Singer of the Southwest Research Institute in Boulder, Colo., of the image, released January 24.
That lack of impact scars suggests that the Kuiper Belt, a reservoir of ancient space rocks beyond the orbit of Neptune, has fewer small objects than scientists expected. If true, that could mean that the precursors to planets grew up fast, without leaving many protoplanetary crumbs behind.
Snapshots taken when New Horizons flew past Pluto and its moons in 2015 showed that those bodies are surprisingly smooth, too. Many of Pluto’s craters could have been covered by geologic activity on the dwarf planet, such as the movement of glaciers (SN Online: 10/15/15). But Pluto’s largest moon Charon is thought to be less active and so shouldn’t erase its craters (SN Online: 7/13/18). Singer and her colleagues have argued that lack of craters meant there were just not that many small objects available to smack into Pluto and Charon.
“If you can’t get geology to erase the craters…
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