In February 2017, researchers announced that the dwarf planet Ceres had organic materials on its surface. Now, a new analysis of NASA’s Dawn data suggests that there might be a lot more of these organic materials than previous studies have suggested.
As reported in Geophysical Research Letters, the team changed the base-line parameter of the analysis. To look for organic molecules, they studied the sunlight bouncing off the dwarf planet's surface. Originally they compared this signal to rocks from Earth, but in the new analysis, the researchers used meteorites for comparison. They claim that it is a better comparison standard.
"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," lead author Hannah Kaplan, from the Southwest Research Institute, said in a statement. "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 6 to 10 percent previously reported based on terrestrial organic compounds."
This study raises new questions about the origin of the organics. Such high abundance, if it actually exists, needs to have an efficient source behind it. Researchers have identified two mechanisms for the high-organic scenario. The first is that they could have been brought to Ceres by comets, which have an organic concentration similar to the one observed in the latest study.
One issue with this approach is that cometary impacts would likely destroy the organic molecules, at least part of them. The other option is that the molecules form deep within the dwarf planet and then migrate toward the surface. It is not clear how this would happen.
"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," added co-author Ralph Milliken, from Brown University. "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."
Organic materials can be formed by living organisms or by chemical processes that have nothing to do with life. The finds from Ceres suggest the potential for complex chemistry on or below its surface. The Dawn mission is currently in its lowest orbit around the object, and will hopefully tell us a lot more about the dwarf planet's composition.