Organic Matter on Dwarf Planet Ceres More Abundant than Thought

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A new analysis of data collected by NASA’s Dawn orbiter suggests that organic molecules may exist in surprisingly high concentrations on the surface of Ceres. The study appears in the journal Geophysical Research Letters.

Organic deposits in Ernutet crater on Ceres. Image credit: Kaplan et al / NASA.

Organic deposits in Ernutet crater on Ceres. Image credit: Kaplan et al / NASA.

Organic molecules are the chemical building blocks for life. Their detection on the dwarf planet Ceres doesn’t mean life exists there or ever existed there; non-biological processes can give rise to organic molecules as well.

But because life as we know it can’t exist without organic material, scientists are interested in how it’s distributed through our Solar System.

The presence of organic material on Ceres raises intriguing possibilities, particularly because the dwarf planet is also rich in water ice, and water is another necessary component for life.

The original discovery of organics on the dwarf planet was made using Dawn’s Visible and Infrared Spectrometer (VIR) instrument.

By analyzing the patterns in which sunlight interacts with the surface, scientists can get an idea of what compounds are present on Ceres.

The VIR instrument picked up a signal consistent with organic molecules in the region of Ernutet crater on Ceres’ northern hemisphere.

To get an initial idea of how abundant those compounds might be, researchers compared the VIR data from Ceres with lab reflectance spectra of organic material formed on Earth.

Based on that standard, they concluded that 6-10% of the spectral signature they detected on Ceres could be explained by organic matter.

But for this the new study, Southwest Research Institute researcher Hannah Kaplan and co-authors wanted to re-examine those data using a different standard.

Instead of relying on Earth rocks to interpret the data, they turned to an extraterrestrial source: meteorites.

Some meteorites have been shown to contain organic material that’s slightly different from what’s commonly found on our own planet.

And the new analysis 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,” Dr. Kaplan said.

“We estimate that as much as 40-50% of the spectral signal we see on Ceres is explained by organics. That’s a huge difference compared to the 6-10% 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 work 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.

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Hannah H. Kaplan et al. New Constraints on the Abundance and Composition of Organic Matter on Ceres. Geophysical Research Letters, published online May 21, 2018; doi: 10.1029/2018GL077913