Planetary Science by Space Missions
Exploring the Subsurface Ocean of Enceladus
One of the most important findings of the Cassini Mission was the discovery that Saturn's small ice moon Enceladus is cryo-volcanically active with a plume from high velocity jets of water vapour and ice particles that emerge from warm fractures in the surface. The analysis of these grains with the mass spectrometer of our dust detector CDA provides the unique opportunity to gather information about subsurface processes below the moon's icy crust. Excitingly our compositional analysis of grains emitted from Enceladus showed that they emerge from liquid water close to the icy surface, that has been in contact with the moon's rocky core at much greater depth (Postberg et al., Nature 2009, 2011). Moreover, silica nano-grains embedded in the ice particles indicated that there is ongoing hydrothermal activity with temperatures of 90°C or more (Hsu, Postberg, Sekine et al., Nature 2015).
We are currently focusing in analyzing the organic material emitted by Enceladus in order constrain the astrobiological potential of this subsurface water world. CDA spectra of icy material emitted by Enceladus subsurface ocean exhibit an abundance of organic material. Due to lack of suitable methodology less than 5% of all E ring spectra have been yet evaluated. In 2017 we will start a refined, systematic CDA spectra evaluation of the entire CDA E ring dataset of over 200.000 ice grain spectra. A newly developed code will automatically recognize ice grain spectra with high abundance of inorganic and organic material. Analogue experiments with out laser assisted mass spectrometer we aim on identification and quantification of the abundant, but currently ambiguous, signatures and relate them to high-mass organic parent molecules.