NASA scientists have taken their first look at the interior of the dwarf planet Ceres, by tracking tiny alterations in the motion of the Dawn spacecraft as it continues to orbit the enigmatic planetoid. These gravitational readings, when paired with the detailed surface data harvested by Dawn, will allow scientists to gain a more comprehensive picture of Ceres' history.
Since arriving in orbit around Ceres in March 2015, Dawn has transmitted countless haunting images of the dwarf planet's barren, cratered landscape. While we have learned a great deal from these images and further data collected from the advanced suite of scientific instruments situated aboard the probe, we have quite literally only been scratching the surface.
A new study led by scientists from NASA's Jet Propulsion Laboratory (JPL) has succeeded in plumbing the depths of Ceres' interior, by analyzing minute alterations in the motion of Dawn as it orbits the dwarf planet.
Any spacecraft in orbit around a solar system body is subject to that object's gravitational pull. A number of factors, including variations in surface height or the density and distribution of the materials that make up the interior of a celestial body, can cause subtle perturbations in the motion of an orbiting spacecraft.
NASA is capable of tracking Dawn's orbital velocity to within 0.004 inches (0.1 mm) of its actual speed by monitoring radio tracking data sent between the probe and the agency's Deep Space Network. The team behind the study was able to analyze these radio signals and isolate orbital alterations caused by variations in Ceres' gravitational field, and by reconciling these gravitational readings with surface observations already collected by the probe, glean insights regarding the composition and structure of the dwarf planet.
It was discovered that Ceres' overall density is significantly weaker than that of other rocky solar system bodies such as Earth, Mars and the asteroid Vesta, which had been Dawn's previous scientific target. According to the analysis of Ceres' gravitational field, it is likely that the dwarf planet is structured in compositionally distinct layers much like Earth, albeit not as well defined.
The densest material on Ceres is located at the planetoid's core, while lighter materials such as water ice are thought to have partially separated from denser rocky material during a heating phase that occurred relatively soon after the creation of the dwarf planet. The lighter matter then gravitated toward the surface to form the planet's outer layers.
The study also confirmed that the structure of Ceres' interior is dictated by the dwarf planet's rotation, thanks to a property referred to as hydrostatic equilibrium, which had been theorized to influence Ceres, but had not been confirmed prior to the study.
The structurally weak nature of Ceres' upper layers causes high elevation features such as the isolated Ahuna Mons to displace material in the planetoid's mantle, much like a large ship would displace water in Earth's oceans. According to the scientists behind the study, it is likely that subsurface water was mobile on ancient Ceres, and that the dwarf planet's interior did not reach sufficient temperatures to melt silicates, and give the planetoid a metallic core.
By combining insights of Ceres' internal structure with the detailed surface analysis carried out by the Dawn spacecraft, scientists can begin to unravel more of the complex formation processes that sculpted the desolate dwarf planet that we see today.