4.9 Rolling on the ground again: MSL
On 6 August 2012, NASA’s Mars Science Laboratory (MSL) rover Curiosity landed in Gale crater at a location called ‘Bradbury Landing’. Gale crater was chosen as Curiosity’s landing site because orbital data, e.g., from the CRISM instrument, had suggested water might once have been present there. Curiosity was fitted with an array of instruments with which to investigate the martian surface and atmosphere, and these have made a number of discoveries relating to water on Mars.
Firstly, Curiosity confirmed the presence of water frost also seen by Viking and Phoenix, and clouds observed by Pathfinder (Figure 45).
Secondly, Curiosity found evidence that water had once existed in Gale crater itself. Very early in its mission, it found conglomerates – rocks made up of rounded pebbles that were transported by water (Figure 46). Careful investigation of the size, rounding and distribution of the pebbles led the mission team to conclude that they were deposited by a stream that was knee to hip deep and probably flowed at an average velocity of 0.20 to 0.75 m s−1. In addition to these conglomerates, sandstones and mudstones were found. The fine-grained nature of the mudstones showed that they settled out from a body of water after coarser grained material had settled out (Figure 47).
Take a look at Figure 48. This shows the minerals found within rocks at Gale crater expressed as pie charts, where the larger the wedge of the pie, the more of that mineral present. The first two pies (lower left of the image, labelled JK and CB) and the last three (upper right of the image, labelled MB, QL and SB) are mudstones.
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Excluding mafic minerals and feldspar, which are common minerals, what is the most common type of mineral shown on the mudstone pie charts?
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In almost all of the mudstone pie charts, clay minerals (green wedge) are the most dominant type of mineral. Haematite (red wedge) is also prominent in some of the charts, as is calcium sulfate (yellow wedge).
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From what you have learned so far, what has led to the presence of clay minerals, haematite and sulfates?
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Clay minerals, haematite and sulfates form in the presence of water by the alteration of existing minerals. Therefore, these suggest there has been water in the Gale crater area.
You will recall that the Spirit rover observed sulfates that were finely dispersed in soils and present as veins within rocks. Curiosity also found these forms of sulfate (e.g., Figure 49), but also observed rocks that contained sulfate as cement holding the grains together. In addition, the ChemCam instrument also found trace elements such as boron and chlorine in some of the sulfate veins, giving further information about the chemistry of the water that formed them (Figure 50).
The results obtained by Curiosity have allowed the science team to reconstruct some of the history of Gale crater. It is probable that the crater was once filled by a lake for an extended period of time. Fresh water flowed into the lake, occasionally from fast flowing streams, which deposited the conglomerates and sandstones. Mudstones were deposited in quieter periods. The lake level fluctuated, and in places there is evidence (e.g., desiccation or mud cracks) that it dried out (Figure 51). This reconstruction allows scientists to understand the changes in climate that might have taken place in Mars’ history and has enabled them to create an animation (Video 3) of the transition between the warmer and wetter Mars evidenced at Gale crater, to the cold and dry Mars that we observe today.
Activity 5: Curiosity on Mars
To date, the Curiosity rover mission has exceeded 3000 sols on Mars, and collected a cornucopia of evidence for past and present water at Gale crater.
Since landing at Bradbury Landing in Gale crater, it has travelled over 20 km across the crater floor, passing by several landmark features such as the Bagnold Dunes and Vera Rubin Ridge. If you would like to find out more about the rover’s traverse and track its current location, you can access this via NASA’s interactive map [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (Figure 52).
