The surfaces, surface processes and materials of objects in our solar systems allow us to determine the history of planets and moons. We are study icy and rocky objects, and investigating their properties by means of laboratory experiments, modelling, and observations (from ground and space-based telescopes). Key targets are rocky planets like Venus and Mars, and icy objects like Titan and Enceladus.
Subsurface ocean and plumes
The Cassini mission revolutionized our vision on the habitability of our solar system. While the icy moons orbiting Jupiter and Saturn were supposed to be cold and inert objects well outside the habitable zone (where water can be found liquid), Cassini showed that Saturn’s moon Enceladus is very active, with a warm interior heated by tidal forces (Porco et al., 2014), allowing the presence of an ocean under a km-thick icy crust (Thomas et al., 2016). This ocean escapes through geysers (plumes) from the icy surface contributing to the formation of an exosphere. Cassini performed many fly-bys through the plumes, measuring their composition and characteristics and showed that the ocean under the icy crust is salty, fed by ongoing hydrothermal activity (Hsu et al., 2015) and contains COMs, i.e. complex organic molecules (Postberg et al., 2018). One possible explanation for this is that the subsurface ocean is covered with an organic film (as this is the case for earth’s oceans) that is carried in the plumes evaporating from the ocean. Another characteristic of the plumes is their very large velocities, reaching 700-900 m/s (Yeoh et al., 2016), highlighting that plumes are due to (an adiabatic) expansion of the gas through a nozzle like crevasse. Is the content of the plume reflecting the sub-surface ocean? Can the characteristics of the plumes (velocities, densities, composition) provide information on the crevasses (depth, thickness) or on the location of the Ocean? To address such questions, we are performing laboratory experiments to understand the relation between liquid ocean and plumes. Plumes are also modelled theoretically, and results compared to experiments and plumes measurements of Enceladus with Cassini.
A close look at the icy surface of Enceladus
In the visible to infrared wavelength range, the light reflected from the surface of an object and collected by spectrometers holds many characteristics on the surface. This reflected light can reveal the objects’ chemical composition, porosity, grain sizes, surface roughness etc. For icy moons, mainly covered by water ice, these characteristics are strongly depending on climate and space weathering, resurfacing, and deposition of gas phase species from plume material. We are expecting for example places covered by plumes material to be covered with amorphous ice, and to have large icy grains. With radiation, the size of the icy grains become smaller. Resurfacing would also produce different ice features. So by looking at Cassini measurements of the reflected light from Enceladus surface, we can separate different processes occurring. Understanding all of the ice features and their evolution is very relevant to understand moons formation and evolution.
Global spectral mosaic using the complete VIMS dataset. The full-colour images were created by combining three IR channels of the VIMS spectro-imager, represented here by red, green, and blue colours, and overlapping these on a mosaic created using the Imaging Science Subsystem on Cassini . The image shows five infrared views of Enceladus centred on the leading side, the Saturn-facing side, and the trailing side in the top row, and the North and South Pole in the bottom row. Image Credit: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute.
Formation of moons of Jupiter and Saturn
The formation of satellites in the environment of Jupiter favored the birth of four large moons with roughly comparable amounts of silicate, but with three of them covered by ices. The presence of ices on these satellites can be explained by the strong temperature gradient that was present in the disk around the giant planet from which the moons formed (Canup & Ward, 2002). For these reasons, they have often been labeled as a miniature solar system. Whereas it is generally accepted that Jovian moons formed from a disk around young Jupiter, it is not the case for Saturn, whose young rings, fast moon tidal migration, and new moons forming in the rings have lead to the belief that many formed later in time.
Possible scenario for the formation of the moons of Jupiter.
Planetary geoscience and meteorites
Understanding how geological materials and landforms leverage our comprehension of planetary evolution. This includes the study of extra-terrestrial materials, such as meteorites, but also the landforms found of planetary bodies. For example, the six ‘Dutch’ meteorites tell a fascinating perspective on primitive, metamorphosed and differentiated planetary bodies; each representing a step in the story (during the first millions of years) of the growth to planethood. However, for the final stages in planetary evolution – spanning the scale of billions of years – landscapes can help us study these processes. Internal and external processes that have affected a planetary surface have caused it to retain clues to the planet’s geologic, climatic, and possibly biologic past. Through meteoritics we study the earliest rocks of our Solar System, while planetary geoscience studies focus more on their lasts transformations; both are highly complementary approaches in the ongoing exploration of our Solar System. Topics that we offer in graduation projects range from e.g. planetary aeolian processes and glaciovolcanism, to more exotic studies of e.g. meteorite aerodynamics. These efforts also offer unique collaborations within our own group as well as with other research groups at TU Delft.