News Feature: “Celestial snowman” starts to reveal its secrets

Nola Taylor Redd

PNAS September 17, 2019 116 (38) 18749-18752

The distant rock has offered clues about planet formation and the state of the early solar system.

Within the cloud of icy rocks at the edge of the solar system lie objects that have remained virtually untouched since their formation more than four billion years ago. Last January, NASA’s New Horizons spacecraft made the first flyby of one such primitive sample, an object known as 2014 MU69 and nicknamed “Ultima Thule” (although that label has proved controversial*). After New Horizons’ successful flyby of Pluto in 2015, researchers were keen to study a primordial body that was within the craft’s reach. With MU69, that dream became a reality. The tiny object, one of only three possible destinations discovered after the mission launched, turned out to be an incredible target. “I really think we hit the jackpot,” says New Horizons principal investigator Alan Stern, of the Southwest Research Institute (SwRI) in Boulder, CO.

Figure: Researchers have started to map out the various geological features of 2014 MU69, including troughs (black lines), scarp crests (notched lines), a feature circling unit mh dubbed “The Road to Nowhere,” and a large crater (lc) dubbed the Maryland Crater. Here, the magenta areas labeled pm are patterned material; green areas labeled rm are rough material, and the blue areas labeled um are undifferentiated material. Image credit: Wikimedia Commons/NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/ESA.

At first glance, MU69 looked much as researchers had imagined a pristine Kuiper Belt object (KBO) would appear, with a dark surface, rich in water ice and organic material, and relatively unscarred by craters. But when they looked closer, it offered plenty of surprises. From its shape to its spin to its composition, the distant rock is providing planetary researchers with a wealth of information about the conditions in the vicinity of the sun 4.5 billion years ago, and it’s even helping solve a decades-old puzzle about how the planets formed.

See https://www.pnas.org/content/116/38/18749