To get an initial idea of how abundant those compounds might be, the original research team compared the VIR data from Ceres with laboratory reflectance spectra of organic material formed on Earth. Based on that standard, the researchers concluded that between six and 10 percent of the spectral signature they detected on Ceres could be explained by organic matter.
But for this new research, Kaplan and her colleagues wanted to re-examine those data using a different standard. Instead of relying on Earth rocks to interpret the data, the team turned to an extraterrestrial source: meteorites. Some meteorites — chunks of carbonaceous chondrite that have fallen to Earth after being ejected from primitive asteroids — have been shown to contain organic material that’s slightly different from what’s commonly found on our own planet. And Kaplan’s work shows that the spectral reflectance of the extraterrestrial organics is distinct from that of terrestrial counterparts.
“What we find is that if we model the Ceres data using extraterrestrial organics, which may be a more appropriate analog than those found on Earth, then we need a lot more organic matter on Ceres to explain the strength of the spectral absorption that we see there,” Kaplan said. “We estimate that as much as 40 to 50 percent of the spectral signal we see on Ceres is explained by organics. That’s a huge difference compared to the six to 10 percent previously reported based on terrestrial organic compounds.”
If the concentration of organics on Ceres is indeed that high, it raises a host of new questions about the source of that material. There are two competing possibilities for where Ceres’ organics may have come from. They could have been produced internally on Ceres and then exposed on the surface, or they could have been delivered to the surface by an impact from an organic-rich comet or asteroid.
This new study suggests that if the organics were delivered, then the potential high concentrations of the organics would be more consistent with impact by a comet rather than an asteroid. Comets are known to have significantly higher internal abundances of organics compared with primitive asteroids, potentially similar to the 40 to 50 percent figure this study suggests for these locations on Ceres. However, the heat of an impact would likely destroy a substantial amount of a comet’s organics, so whether or not such high abundances could even be explained by a cometary impact remains unclear, the researchers say.
The alternative explanation, that the organics formed directly on Ceres, raises questions too. The detection of organics has so far been limited to small patches on Ceres’ northern hemisphere. Such high concentrations in such small areas require an explanation.
Organics were recently detected on the dwarf planet Ceres with infrared spectroscopy. The origin of these organics is, as yet, unknown. Using laboratory spectra of terrestrial and extraterrestrial (meteorite‐derived) organic materials with known composition, we reanalyze the Ceres spectra to constrain composition and abundance of those organics. Such constraints could help us discern whether these organics formed on Ceres or were delivered by an impactor.