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Ultima Thule is lumpy, and scientists aren't sure why.
Just after midnight on Jan. 1, NASA's New Horizons spacecraft zoomed past Ultima Thule, a small, frigid object that lies about 1 billion miles (1.6 billion kilometers) beyond the orbit of Pluto.
New - Horizons - Encounter - World - Km
The photos New Horizons captured during that epic encounter revealed a world unlike any other ever seen up close. The 21-mile-wide (33 km) Ultima Thule is bilobed and therefore resembles a reddish snowman — if that snowman had been flattened like a pancake.
"These are not spherical lobes at all," New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, said Tuesday (April 23) during a presentation at the Outer Planets Assessment Group meeting at NASA headquarters in Washington, D.C.
Surprise - Stern - Everybody - Surprise
"That caught us by surprise," Stern added. "I think it caught everybody by surprise."
"They seem to be raised, but exactly what causes them we're not sure," Stern said. "It's still early days."
Hypothesis - Mounds - Convection - Ice - Heat
An early hypothesis held that the mounds resulted from convection of low-temperature ice, which was driven by the heat generated by the radioactive decay of aluminum-26. But further work suggests that this is an unlikely scenario, Stern said. The team now thinks the mounds may be the retained outlines of the small planetesimals that came together to form the Ultima lobe long ago.
"But there could be other processes as well," Stern said. "So, this is an active topic of debate."
Ultima - Thule - Cloud - Material - Sun
Ultima Thule coalesced from a cloud of rocky, icy material far from the sun. These smaller chunks first formed two larger objects, which then apparently orbited a common center of mass as a binary pair, Stern said. These two bodies then slowly merged to form Ultima Thule (which is officially known as 2014 MU69).
The mission team...
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