Pluto’s twin Eris found to be ‘soft’

About 18 years ago, astronomers detected a miniature, icy world called Eris billions of kilometers beyond Neptune. But unlike its dwarf planet cousin Pluto, which New Horizons introduced as a rich and dynamic world after its visit in 2015, Eris has not had any robot visitors. In fact, it is so far from Earth that it appears as just a single pixel of light in observations. As a result, scientists know very little about what’s going on on Eris. At least so far.

Due to its location near the edge of the Solar system, Eris is known to be extremely cold and snow falls on its surface. Thanks to data collected from new observations for Eris, which is approximately 68 times farther from the Sun than the Earth, more details about the planet have been revealed.

“Soft as cheese”

It appears that residual heat from the dwarf planet’s birth is leaking out and slowly stretching its icy surface. This process causes Eris to behave less like a solid, rocky planet and “more like a soft cheese or something like that,” study co-author Francis Nimmo of the University of California Santa Cruz said in a statement. While much is still unknown about Eris, it is considered an “almost perfect” twin of Pluto, as both dwarf planets are almost exactly the same size. In fact, when it was first detected in 2005, it appeared slightly larger than Pluto, triggering a debate among scientists. This situation led the International Astronomical Union (IAU) to clarify the definition of planet and downgrade Pluto to the dwarf planet class.

In the latest study, a mass estimate was also made for Eris’ very small moon Dysnomia. Eris and its moon were found to be mutually gravitationally locked to each other, meaning they are both pointing in the same direction towards each other. The new findings suggest that Eris likely has a rocky core surrounded by an icy crust. Researchers say radioactive elements in the planet’s interior produce heat, which slightly melts the ice on the surface. For this reason, they expect Eris’s surface to be extremely smooth, as surface features such as craters will be covered by flowing ice.

Although modeling with new data has provided important information about Eris, what we know about this dwarf planet is still quite limited. Researchers state that Eris needs to be examined more closely both to discover the reliability of the models and to learn more.