PROVIDENCE, R.I. [Brown University] — Scientists working with NASA’s Dawn mission have discovered the presence of organic material — basic building blocks of life —on the dwarf planet Ceres, the largest object in the asteroid belt between Mars and Jupiter.
The findings, published on Feb. 16 in the journal Science, don’t necessarily mean Ceres has or ever had life, but they do indicate a “complex chemical environment [on Ceres], suggesting favorable environments for prebiotic chemistry,” the researchers say. The discovery is the newest surprise turned up by the Dawn spacecraft, which entered orbit around Ceres in 2015. Dawn has already found evidence of water-rich clay minerals Ceres’s surface as well as carbonate minerals indicative of active hydrothermal processes beneath the surface.
This latest finding marks the first definitive detection with a modern spacecraft of organics in the asteroid belt, says Carlé Pieters, co-investigator on the Dawn mission and a professor in the Department of Earth, Environmental and Planetary Sciences at Brown University. She discussed the new findings in an interview.
How would you characterize the significance this discovery?
Organic molecules are among the ingredients necessary for life. Some of the biggest questions in space and planetary science deal with the distribution of organics in the solar system. Where did they come from? How were they formed? How do they relate to the evolution of life? This discovery adds an important piece to the puzzle.
What we’ve found on Ceres is probably the most unambiguous detection of organics on any solar system body other than Earth. We’ve collected meteorites on Earth with organic signatures, which makes us think their parent asteroids may have had organics. But until now we haven’t seen such definitive evidence on any asteroid. So this could help us put together the history of organics in the solar system.
How was the detection made?
It was done using the visible and infrared mapping spectrometer developed by our Italian colleagues, which is flying on the Dawn spacecraft. The instrument analyzes the light reflected from the surface, looking for specific parts of the spectrum where the surface reflectivity varies in a characteristic pattern. That can tell us something about the composition of the surface. There’s a highly diagnostic absorption feature for organics at a wavelength of 3.4 microns, and we saw that signal very clearly on Ceres. But it’s not everywhere. It’s very localized across a particular region.
Can you describe that region and where the deposits are within it?
We made the detection in an area in the northern part of Ceres, near a crater called Ernutet. It’s a heavily cratered area, which means it’s a well developed, fairly old surface. The organic deposits are scattered through the Ernutet region. Some of deposits are very tight and localized. Some are more diffuse. So it’s not a uniform distribution. It’s more scattered.
Is there a sense of where these materials came from?
It’s hard at this point to say for certain, but we do have some hypotheses. There’s some reason to suspect that these formed internally within Ceres and were brought to the surface. One of the other big surprises to come out of the Dawn mission had to do with strange-looking extremely bright areas we detected in another crater called Occator. Those small spots turned out to be concentrations carbonate minerals, probably extruded onto the surface along with some kind of volatile material. As the volatiles were lost into space, we were left with these carbonate deposits. That finding clarified the idea that there are hydrothermal processes going on within or below the crust of Ceres. So it makes a well-integrated hypothesis that these organics could have been created by internal processes and later exposed on the surface as well.
That’s one good hypothesis, but it’s not the only one. It’s possible, for example, that these materials could have been delivered to Ceres as a cloud of debris from an external source traveling through the solar system. There are high-resolution data available from Dawn that provide the geologic context for these deposits. We’re looking at those data now, which will help us to pin down the origin of these materials.
What does this say about the possibility of life on Ceres?
Even before we sent the Dawn spacecraft to Ceres, we knew by its low density that it probably had lots of water ice beneath its surface. Since then, Dawn has found clay minerals virtually everywhere on Ceres as well as ammoniated minerals and evidence of local hydrothermal activity. Now we’ve added organics. Together, those are the essential ingredients for life. However, it doesn’t mean life existed on Ceres. It’s kind of like baking a cake. You can have all the ingredients, but if you don’t put them together properly, you don’t end up with a cake. So there is still plenty of work to be done before we can start thinking about whether microbes were able to form on Ceres.
Altogether, it’s an exciting discovery and we’re certainly looking forward to investigating it further.