Ceres's surface may have high levels of organic compounds

Organics could have originated within the dwarf planet or have been delivered by comets and asteroids.
By Laurel Kornfeld | Feb 07, 2019
A new analysis of data returned by NASA's Dawn spacecraft suggests Ceres's surface contains a significantly higher level of organic compounds than mission scientists initially thought.

Dawn's Visible and Infrared Spectrometer (VIR) discovered organic materials on Ceres by analyzing the wavelengths of sunlight the dwarf planet reflects and absorbs. Specifically, it detected a signal associated with organic molecules on Ceres's northern hemisphere, in the region around Ernutet Crater.

While organic molecules are the building blocks for life, their presence is not sufficient to indicate whether life, past or present existed on the dwarf planet. Organics can be produced by both biological and geological processes.

However, organic compounds, as well as water, must be present for life to exist anywhere. The fact that Ceres has both organic compounds and is rich in water ice means makes it an enticing place for further study.

In an effort to determine the level of organics on Ceres, mission scientists compared VIR data with reflectance spectra of organic compounds on Earth and found between six and ten percent of Ceres's spectral signature to be coming from organic material.

Now, researchers at Brown University in Providence, Rhode Island, led by Hannah Kaplan of the Southwest Research Institute (SwRI) in San Antonio, Texas, re-examined the Dawn data by comparing Ceres's spectral signatures with those of meteorites, which originated beyond Earth.

Many meteorites composed of carbonaceous chondrites came from primitive asteroids, whose organic compounds are somewhat different from those found on our planet.

"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 noted.

"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."

High levels of organics on Ceres could have two possible sources. They could either have been produced within the dwarf planet and subsequently exposed on its surface, or they could have been delivered by organic-rich comets and/or asteroids.

"If the organics are made on Ceres, then you likely still need a mechanism to concentrate it in these specific locations or at least to preserve it in these spots. It's not clear what that mechanism might be. Ceres is clearly a fascinating object, and understanding the story and origin of organics in these spots and elsewhere on Ceres will likely require future missions that can analyze or return samples," said Ralph Milliken of Brown University.

A paper on the latest findings has been published in the journal Geophysical Research Letters.

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