Ancient interior activity likely formed features on Ceres’ surface
A new analysis of surface features on Ceres sent back by NASA’s Dawn spacecraft indicates that at least some of those features were created by the ancient movement of materials in the dwarf planet’s interior. The study centers on linear features; specifically, chains of secondary craters and small pits.
While primary craters are produced directly by impacting objects, secondary craters are formed from materials ejected from the former and often surround them in clusters or rays.
However, pit chains are produced by fractures beneath the surface resulting from interior geological activity.
For the study, scientists produced a map showing all features on Ceres with minimum lengths of 0.6 miles (one kilometer) outside of impact craters.
The map depicted more than 2,000 such features. Because chains of secondary craters and chains of small pits share many common characteristics, the researchers’ most difficult task was distinguishing between the two categories.
Secondary crater chains are usually composed of round sunken areas made by fragments ejected from primary craters. The more common of the two features, they are typically positioned in long strings, with each crater surrounded by a rim. Whereas pit chains are less round than secondary craters and more irregularly shaped. Individual pits do not have raised rims.
Distinguishing between the two types of linear features is important because only the pit chains are created by Ceres’ interior activity, meaning they alone hold keys to the dwarf planet’s interior evolution.
The pit-chains’ presence indicates that the dwarf planet’s interior has had an active geological past.
Sometime between several hundred million and one billion years ago, subsurface materials within Ceres’ interior welled upward, in the process making fractures in the crust.
Scientists think the interior material that welled upward was less dense than that which surrounded it. The pit chains resulted from the fracturing of surface material.
“As this material moved upward from underneath Ceres’ surface, portions of Ceres’ outer layer were pulled apart, forming the fractures,” explained Jennifer Scully, member of the Dawn science team and lead author of a paper on the findings published in the journal Geophysical Research Letters.
Evidence of interior upwelling is an important detail for scientists seeking to trace Ceres’ evolution.
Other possible scenarios have been considered as explanations for Ceres’ linear features but subsequently dismissed as unlikely.
One such scenario attributes the features to the freezing of a subsurface ocean. However, that would have caused the pit chains to be scattered evenly across the dwarf planet’s surface, which is not the case.
Other studies of Dawn data show evidence Ceres may still have a subsurface liquid ocean.
Another possibility is the fractures were created by stresses from a large impact. However, impacts capable of generating such fractures would have left behind evidence, and no such evidence was found on Ceres.
Scientists conducting further research on Ceres’ geological evolution will incorporate this study’s findings into computer models in an effort to find evidence that interior upwelling occurred close to the surface fractures.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.