The Colour and Stereo Surface Imaging System (CaSSIS) onboard the ExoMars Trace Gas Orbiter mission returned this image of an area in Melas Chasma, part of the vast Valles Marineris canyon system on Mars. Valles Marineris stretches for more than 4000 km across the planet’s surface, and plunges more than 7 km deep in places.

The section seen here is about 5 x 6 km in size. It is a colour infrared image (combining the NIR, PAN and BLU filters of CaSSIS), and emphasizes the spectral diversity of landforms and sediments on the surface. It shows details of a blocky deposit on the floor of Melas Chasma that is consistent with an eroded and exposed landslide deposit. Windblown ripples are abundant and interspersed between the blocks.

The CRISM spectrometer on NASA’s Mars Reconnaissance Orbiter revealed a variety of minerals and phases that correlate with the light-toned blocks seen here (for example: nontronite, jarosite, aluminium-rich clays, hydrated silica, and/or an acid-leached clay). The tan-coloured ripples likely contain ferric iron oxides that gives rise to this distinctive colour. There is also evidence of the past presence of water in this region. The bright-white layered materials imply the presence of a hydrated calcium sulphate (possibly gypsum), which is thought to have formed through the ponding and subsequent evaporation of water that may have once occupied portions of the Chasma floor.

The image was taken on 19 October 2020 and featured on the February 2021 cover of Nature Geoscience.

The ExoMars programme is a joint endeavour between ESA and Roscosmos.