The space snowman known as 2014 MU69 or Ultima Thule added to its celebrity today by showing up on the cover of the journal Science, with the first peer-reviewed results from an encounter with NASA’s New Horizons spacecraft laid out within.
Close study of the two-lobed object — which orbits 4 billion miles from the sun within a sparse belt of icy material known as the Kuiper Belt — could shed light on how the solar system was formed, said New Horizons principal investigator Alan Stern, a planetary scientist at the Southwest Research Institute.
“We’re looking into the well-preserved remnants of the ancient past,” Stern said in a news release. “There is no doubt that the discoveries made about Ultima Thule are going to advance theories of solar system formation.”
Most of the findings published today came out informally in the aftermath of New Horizons’ flyby on New Year’s Day, but the research paper summarizes everything that’s been learned to date — and points to mysteries yet to be solved.
For example, take that snowman shape: Closer analysis of the data found that the two lobes of Ultima Thule are shaped more like a walnut and a hamburger than like two snowballs. The broader, flatter lobe, known as “Ultima,” measures roughly 13.6 by 12.4 miles wide and just 4.3 miles thick. The walnut-shaped lobe, called “Thule,” is 8.7 by 8.7 by 6.2 miles. Put together, the two lobes measure about 22 miles from end to end.
Thule’s dominant feature is a 5-mile-wide impact crater that’s been nicknamed Maryland, in honor of the state where New Horizons’ mission control is located (at Johns Hopkins University’s Applied Physics Laboratory, to be exact).
But Ultima seems to be a crazy quilt of surfaces. That could suggest that the cosmic hamburger coalesced from an assortment of smaller planetesimals. “Whether they are a relic of Ultima’s formation or a result of a later evolution is unclear,” the authors write.
Scientists figure that Ultima and Thule were once separate objects that orbited each other, and were gently pulled together by their mutual gravitational attraction. The orbital momentum of the two objects must have dissipated somehow — but researchers haven’t yet figured out how that happened. Was it through interaction with primordial gas in the early solar nebula, or by the ejection of material that served to shrink their orbit?
Ultima Thule ranks as one of the reddest objects in the outer solar system studied at close range, That’s thought to be due to the chemical modification of organic materials on the object’s surface. Preliminary findings indicate that Ultima Thule’s surface contains an unusual mix of methanol, water ice and organic molecules.
Some of the scientific mysteries may be solved when more detailed readings are beamed back from the New Horizons spacecraft’s memory banks. The study published today was based on only about 10% of the total data collected during the flyby, and today that figure is still in the range of just 25%. Transmissions are expected to continue into late summer of 2020.
New Horizons made history back in 2015 when it flew past Pluto, and Ultima Thule represents the second act of what is now a 13-year space mission. There’s likely to be a third act ahead: The piano-sized probe is speeding outward at nearly 33,000 mph and keeping its eye on more objects in the Kuiper Belt as it flies past at a distance. By the time New Horizons is finished sending back all the data from Ultima Thule, Stern and his colleagues are hoping to identify yet another target for a close flyby.
More than 200 researchers are listed as co-authors of the open-access Science paper, titled “Initial Results From the New Horizons Exploration of 2014 MU69, a Small Kuiper Belt Object.” Notable co-authors include NASA Associate Administrator Thomas Zurbuchen, NASA Planetary Division Director Lori Glaze, NASA chief scientist Jim Green and legendary Queen guitarist Brian May, who happens to be a Ph.D. astrophysicist specializing in stereo imagery.