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Projet ROCOCO : Research On the Cerean Organic Carbon Origins

publié le , mis à jour le

Dr. V. Vinogradoff
Collaborations : Dr. Maria-Cristina De Sanctis (IAPS-INAF, Rome), Dr John Brucato (Arcetri-INAF, Florence), G. Poggiali ((Arcetri-INAF, Florence), Dr. Julie Castillo-Rogez (JPL, Pasadena), Dr. Marc Neveu (NASA, Goddard).

This projet aims to determine the nature and the origin of the organic matter observed with the Dawn mission on Ceres, the biggest asteroid of the main belt (classified as dwarf planet). This is the first time that such important fingerprint of organic matter are observed at the surface of a main belt object. Understanding its composition and origin is challenging for organic matter issues in the primitive solar system objects.

Dawn is a mission from the NASA, launched in 2007 to study the two main bodies of the asteroid belt, Vesta and Ceres, two objects recalled as protoplanets or dwarf planets.
After a very successful observation and characterization of Vesta, Dawn approach Ceres and entered in its orbit the 6th of march 2015.
Instruments onboard the Dawn spacecraft reveal an extraordinary world. Ceres appears to be a very complex water-rich world with no clear correspondence to asteroid fragments (meteorites) on Earth. Its surface is covered by phyllosilicates, carbonates, ammoniated-bearing hydrated minerals, water ice, salts and opaque materials, indicating a complex evolution. The two white spots, first things observed during the orbital approach, are a fresh excavation of carbonates, in the center of a big crater, Occator.

Figure 1 : Ceres both sides (false Color - Credit : NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

All the chemical characterizations are mainly obtained from the Visible and InfraRed (VIR) mapping spectrometer onboard the Dawn spacecraft, built by the Italian agency.

Figure 2 : VIR spectrometer onboard the Dawn spacecraft (credit NASA/JPL/INAF-IAPS)

While the spacecraft was operating in the north, VIR aquired data that revealed the presence of abundant aliphatic carbons localized near the Ernutet crater, thanks to the broad band observed in the 3.3-3.6 µm spectral range.

Figure 3 : Organic matter observed around Ernutet crater with the spectra from VIR (enhanced colors from the framing camera). (Credit De Sanctis et al, Science, 2017, Pieters et al., MPS, 2017)

This spectral range is particularly suitable for the detection of organic matter, where infrared absorptions from CH, NH, OH and even CO3 can be observed and are not hidden by the 3 µm absorption feature of water inside silicate (OH) and/or ammonium ion (NH4+).

Although these aliphatic features are uncommon on asteroid bodies, they are not unique to Ceres, and have also been remotely observed in two other bodies, namely 24 Themis and 65 Cybele. Nevertheless, the nature of this OM on Ceres is unknown. The exogenous or endogenous sources of this OM in Ceres are still under investigation but several hints (quantity, geological features) weigh for an endogenous source.

The signature of this organic matter is similar to organic material composed of aliphatic carbons but also aromatic carbons with a rather small proportions of heteoratoms, and for example fits organic matter spectra such as asphaltite, oil, and insoluble organic matter in meteorites. The quantity of this OM seems to be at least three time more abundant that the one in carbonaceous chondrites ( >15 %wt) and so raise question about its origin. Experimental and simulation investigations are on going to find more about this organic matter on Ceres.


Insight into the abundance and origin of aliphatic carbons observed on Ceres
V. Vinogradoff, G. Poggiali, J. Brucato, A. Raponi, M. Ciarniello, S. De Angelis, M. Ferrari, E. Ammannito and M.C. De Sanctis.
Abscicon conference abstract,
Publication in preparation.

Sources and Sinks of Carbon Inside Ceres.
Castillo-Rogez, J. C., Vinogradoff, V., De Sanctis, M. C., Hesse, M., Marchi, S., Neveu, M., ... & Raymond, C. A. (2019). In Lunar and Planetary Science Conference (Vol. 50).
Publications in preparation

An aqueously altered carbon-rich Ceres
S. Marchi, A. Raponi, T. H. Prettyman, M. C. De Sanctis, J. Castillo-Rogez, C. A. Raymond, E. Ammannito, T. Bowling, M. Ciarniello, H. Kaplan, E. Palomba, C. T. Russell, V. Vinogradoff & N. Yamashita (2019), Nature Astronomy, 3, 140-145.

Characteristics of organic matter on Ceres from VIR/Dawn high spatial resolution spectra.
De Sanctis, M. C., Vinogradoff, V., Raponi, A., Ammannito, E., Ciarniello, M., Carrozzo, F. G., ... & Russell, C. T. (2018). Monthly Notices of the Royal Astronomical Society, 482(2), 2407-2421.