Free Astronomy Magazine March-April 2021

MARCH-APRIL 2021 MARS ROVERS T his view of Hot- tah is a mosaic of images taken by the right (telephoto-lens) camera of the Mast- cam on Curiosity dur- ing the 39 th Martian day, or sol, of the rover’s work on Mars (Sept. 14, 2012 PDT/ Sept. 15 GMT). Here, billions of years ago, a stream flowed. [NASA/JPL-Caltech/ MSSS] so that the individual elements in both sce- narios have smoothed and rounded surfaces from mutual collisions and rolling in torren- tial shores. Very inter- esting is also the fact that Hottah shows ev- ident traces of ero- sion following its lift- ing from the ground, which suggests that the slab (1) was formed as a result of sedimentation of ma- terial carried by wa- ter, (2) was then hit by a meteorite that lifted it from the stream bed and (3) was subsequently eroded by the water that continued to flow above it. As shown by the images presented here, on the front of the slab crack there are some small but clearly blunted pebbles and part of the gravel has fallen below the fault to form a small de- posit. This scenario indicates a slow washout of the sandy matrix. Some grooves left by the last streams of water in and around the rocky out- crop are also clearly visible, a sign of a gradual drying up of the stream. Researchers estimate that thou- sands of years, if not millions, are needed to create a landscape with Hottah characteristics, confirming that the flow of water on Mars was not an ephemeral phenomenon. From the size and shape of the con- glomerate rocks, and from the size of loose gravel and pebbles, infor- mation can be obtained on the speed and depth of the stream’s water. Geologists at the Planetary Science Institute, engaged in the in- terpretation of what Curiosity dis- covered, are inclined to believe that the water reached, depending on the points of the stream, heights of between a few centimeters and al- most a meter, and that its speed was about 1 m/s. Only a water- course of this capacity would have