"Detecting Ultima Thule's Size and Shape on Approach" by NASA / Public Domain

The Hunt Is On for Moons Around Ultima Thule

Jan 4, 2019

By Mike Wall

The most distant celestial object ever explored may well have moons, and astronomers are trying hard to find them.

In the wee hours of Jan. 1, NASA’s New Horizons spacecraft zoomed past the small, frigid object Ultima Thule, which lies more than 4 billion miles (6.4 billion kilometers) from Earth. The probe has beamed home just a tiny fraction of its flyby data so far, but mission team members are already starting to get the goods on the far-flung rock.

For example, scientists now know that the 21-mile-long (33 km) Ultima Thule is composed of two roughly spherical lobes, which apparently began their lives as independent, free-flying objects. The duo quickly spiraled closer and closer together, joining up in the solar system’s earliest days to form a reddish “snowman.”

Modeling work suggests that the two constituent bodies, dubbed “Ultima” and “Thule,” likely completed one rotation every 3 or 4 hours around the time when they hooked up, mission team members said. But New Horizons’ observations show that the present-day Ultima Thule takes about 15 hours to make a full spin.

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