Dwarf Planet Ceres Has Carbon-Rich Surface, Study Suggests

The surface of the dwarf planet Ceres may contain several times the concentration of carbon than is present in the most carbon-rich, primitive meteorites found on Earth, according to a new study published in the journal Nature Astronomy.

This false-color image shows the dwarf planet Ceres. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

Ceres is believed to have originated about 4.6 billion years ago at the dawn of the Solar System.

Data from NASA’s Dawn spacecraft previously revealed the presence of water and other volatiles, such as ammonium derived from ammonia, and now a high concentration of carbon.

This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter.

An ensuing shakeup in the orbits of the large planets would have pushed the dwarf planet to its current location in the main asteroid belt.

“With these findings, Ceres has gained a pivotal role in assessing the origin, evolution and distribution of organic species across the inner Solar System,” said lead author Dr. Simone Marchi, a researcher at Southwest Research Institute.

“One has to wonder about how this world may have driven organic chemistry pathways, and how these processes may have affected the make-up of larger planets like the Earth.”

Marchi et al constructed a possible schematic path for the evolution of Ceres’ upper crust. The figure shows the presence of carbonaceous chondrite-like materials (black) mixed with products of aqueous alteration such as phyllosilicates, carbonates and magnetite (green) and organics (orange). Shaded blue regions indicate water, and blue lines represent conduits for water migration. Organics may have formed in place during aqueous alteration or could have been concentrated by fluids ascending to the upper crust, resulting in the inferred higher-than-chondritic carbon concentration on Ceres’ surface. Over time, the surface gets homogenized by mixing due to collisions and other processes. Image credit: Marchi et al / Southwest Research Institute.

Geophysical, compositional and collisional models based on Dawn data revealed that Ceres’ partially differentiated interior has been altered by fluid processes.

The overall low albedo of the dwarf planet’s surface is a combination of rock-water interaction products such as phyllosilicates and carbonates and a significant amount of spectrally neutral darkening agents, such as an iron oxide called magnetite.

The Dawn data also point to the presence of an additional darkening agent, probably amorphous carbon, a carbon-rich organic material.

Interestingly, specific organic compounds have also been detected near a 31-mile (50 km) wide impact crater named Ernutet, giving further support to the widespread presence of organics in Ceres’ shallow subsurface.

According to the new study, 50-60% of Ceres’ upper crust may have a composition similar to primitive carbonaceous chondrite meteorites.

This material is compatible with contamination from infalling carbonaceous asteroids, a possibility supported by Ceres’ battered surface.

“Our results imply that either Ceres’ accreted ultra-carbon-rich materials or that carbon was concentrated in its crust,” Dr. Marchi said.

“Both potential scenarios are important, because Ceres’ mineralogical composition indicates a global-scale event of rock-water alteration, which could provide conditions favorable to organic chemistry.”

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S. Marchi et al. An aqueously altered carbon-rich Ceres. Nature Astronomy, published online December 10, 2018; doi: 10.1038/s41550-018-0656-0