HMT production and sublimation during thermal process of cometary organic analogs. Implications for its detection with the ROSETTA instruments

We characterized the organic residue thermal evolution for temperatures up to 500 K. We observed that HMT is still produced at temperatures higher than 300 K. Production of solid HMT and sublimation are simultaneous. HMT observed in the solid phase could be only a minor fraction of the total HMT production, the major fraction being sublimated. The kinetics of the HMT thermal evolution strongly depends on the organic residue composition at 300 K and seems to depend on the exact nature of the oxygenated fraction of the organic residue. The maximum temperature at which solid HMT is observed is 450 K. As HMT forms only for temperatures greater than 280 K in laboratory conditions, it implies that the detection of solid HMT in extraterrestrial samples will provide a strong indication of their thermal history. Consequently, the search for HMT in both solid cometary grains and gaseous phases in the coma of Comet 67P/Churyumov-Gerasimenko will have to be performed by the Rosetta space mission, in particular with the COSIMA and ROSINA instruments.