Astronomers who compared the data taken by Dawn with models of Ceres on Earth determined that the organic matter on its surface came from Ceres itself.
This image of Ceres was captured by the Dawn spacecraft. The bright area in the center is Occator Crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The dwarf planet Ceres is one of the most enigmatic worlds in our solar system, one whose secrets scientists have only been discovering in the last decade. When NASA's Dawn mission arrived in 2015, it discovered an active, salt-rich world that could have, or once had, an ocean. Now, new research provides evidence that it might also contain just the right amount for life.
In an article published Wednesday in Scientific advancesResearchers present evidence that a series of chemicals called long-chain aliphatic organics (AOs), basically long chains of hydrocarbons that often form natural lipids (fats), may have formed inside Ceres and come to the surface through through cryovolcanism.
Related: Explore the icy secrets of Ceres
A world in evolution
Before this study, scientists knew that there were AO on Ceresbut it was not clear whether they had been deposited on the surface by meteorites or were already present. This last idea reinforces the idea that Ceres was once an ocean world, as similar compounds are found on other water worlds such as Enceladus. The relative abundance of these chemicals on Ceres was also too high to come from meteorites alone.
Ceres is the largest object in the main belt. And it doesn't look much like other objects there; Scientists believe it may have formed further out in the solar system, closer to the Kuiper Belt, where other dwarf planets such as Pluto and Eris reside. It may have once hosted an ocean that lasted hundreds of millions of years, and may now exist only in pockets beneath deposits of muddy brines closer to the surface.
OCs degrade rapidly, in about 10 million years. That means the AOs seen on the surface of Ceres must have formed recently. Additionally, AOs are found near sites that have other evidence of plume-like activity.
“Ceres is a geologically active world. We have identified very recent (in geological time) mountains, domes and fractures, says lead author María Cristina De Sanctis, a planetary scientist at INAF-Istituto di Astrofisica e Planetologia Spaziali in Italy. “The presence of AOs that should be recent, or otherwise unobservable, confirms that Ceres can be considered a still evolving body.”
Creating a mini-Ceres
To determine why they were seeing such high concentrations of OAs, the team took the Dawn data and compared it to a recreation of Ceres-like conditions in a lab. This mini-Ceres was given AOs and then subjected to the various types of radiation that would be expected in interplanetary space near its orbit around the Sun. The team tracked the breakdown of the AOs to estimate when the currently observed AOs they could have reached the surface, as well as to determine their origin. Based on their results, the team believes that AOs buried beneath the surface were exposed over time, reinforcing the idea that they came from the depths of Ceres' ocean, rather than meteorites from above.
The results also showed that the current abundance is likely the result of even larger amounts of OA being pushed to the surface, with some breaking down before more rose.
And, if Ceres had an ocean, that ocean could have once supported life. De Sanctis says the presence of clays, carbonates, salt water, ice, salt and organic substances points to the main belt world having the right chemicals. And OAs help strengthen the case.
“In particular, the large amount of AO and the type of AO (spectrally similar to terrestrial kerogens (containing detritus of dead organisms)) increase the potential of Ceres in terms of habitability,” he says.
Our understanding of the many ocean worlds in our solar system is just beginning. Although researchers are still sifting through the wealth of data from the now-completed Dawn mission, the new mysteries they've uncovered on such a nearby world could mean another closer look will soon be necessary.
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