Matthew Read
The Colour and Stereo Surface Imaging System (CaSSIS) is a surface imager aboard the European Space Agency’s ExoMars Trace Gas Orbiter (TGO), which was launched to Mars in March 2016. CaSSIS acquires high resolution images (4.6m/pixel) of the Martian surface in four different wavelength bands simultaneously, allowing for colour images to be generated. Stereo images are also possible with CaSSIS, due to an inbuilt novel rotation mechanism. CaSSIS aids the TGO in it’s search for signs of past and present life on Mars, by investigating surface geology composition and evolution, looking for past and present signs of water and tracking possible sources of atmospheric trace gases. CaSSIS also provides support for future missions to Mars, by characterizing the suitability of potential landing sites. In this poster, I will describe how CaSSIS operates, from image planning to acquisition, showing some recently acquired images of the Martian surface along the way!
Both stages aim to address the primary goal of ExoMars in separate ways. The rover by directly analyzing material on the surface of Mars and the TGO by analyzing the composition of the atmosphere, investigating surface geology composition and evolution and looking for particles associated with the presence of surface water.
CaSSIS aids the TGO in it’s investigations by taking images of the Martian surface in 4 separate wavelength bands at a resolution of 4.6m/pixel. CaSSIS is a push frame imager, which means that a series of sub-exposures are taken in a single observing sequence. These sub-exposures are then stitched together in each filter to create four separate images. Images in different filters are then combined together to create a colour image.
Due to the novel rotation mechanism on CaSSIS, the telescope can be rotated 180 degrees in roughly 30 seconds. This allows CaSSIS to take an image of a surface target as the TGO flies both towards and away from the target. Since the target is observed from two different perspectives, a 3d or stereo image can be generated. This vastly improves on previous Martian imagers, as it is common for stereo images to be created using individual images that have been acquired at vastly different times.
Images are planned with CaSSIS using specialist software. Targets on the surface of Mars are suggested by a team of scientists. For a given period of observing time, these suggested targets are filter to see which are observable. Using a scientific priority associated with each suggested target, images are planned and turned into commands for CaSSIS to execute.
Some of the favorite CaSSIS images are regularly being published on the twitter and Instagram associated with CaSSIS. Regular press releases by ESA also show recent favorites acquired with the instrument.