Icy worlds’ secrets
The distant dwarf planet Eris is nearly the same size as Pluto and occupies the same frozen region of our outer solar system, called the Kuiper Belt. It’s so distant that trying to collect data through telescopes poses many challenges. However, a research team published a new paper in Science Advances Nov. 15 demonstrating that by studying how Eris’ moon, Dysnomia, affects its parent body as the two orbit each other, researchers can uncover clues about the internal makeup of this distant world.
Pluto and Eris dominate the Kuiper Belt, with the latter just 30 miles (48 kilometers) smaller in diameter than the former. Each has at least one satellite large enough to exert influence on its parent body as the two orbit a mutual center of mass. Francis Nimmo, a planetary scientist at the University of California, Santa Cruz, says that just as Earth’s Moon slowed our planet’s early rotation rate, the same thing happened with Eris; resulting in Dysnomia and Eris becoming tidally locked.
Analysis of the orbits of Eris and Dysnomia revealed that, based on how the system has evolved, Eris must be differentiated into a denser core and a less-dense crust. Dysnomia is rather small, so for it to have spun Eris down, Eris must be “squishy,” with a composition that isn’t all hard rock all the way through — i.e., it must have an icy mantle or even an ocean above a more solid, rocky core. This is identical to Pluto, which astronomers believe hosts a liquid ocean beneath its top layer of ice. Ultimately, the study shows that distant bodies like Pluto and Eris, once thought to be rocky, dead worlds, may not be as “boring” as once thought. However, determining which have liquid oceans is still difficult, if not impossible. Nonetheless, “I think the lesson from Pluto is that even out there, oceans are things we should be thinking seriously about,” Nimmo said.