Cosmos - - Holodeck -

Mars is pock­marked by tow­er­ing moun­tains such as Olym­pus Mons – three times the height of Mount Ever­est – and craters 9 km deep. The mass dif­fer­ences in the crust mean space­craft ex­pe­ri­ence tiny changes in grav­i­ta­tional tug as they or­bit Mars. Th­ese wob­bles are mea­sur­able and can be used to cal­cu­late the chang­ing grav­ity and mass. For in­stance, they re­vealed that the mass of the CO2 ice­caps varies sea­son­ally by 4 tril­lion tons.

Sci­en­tists pooled mea­sure­ments from three or­biters to build this grav­ity map of the planet in 2016. Low- grav­ity canyons like Valles Marineris in blue (cen­tre) stand out from the high- grav­ity reds and whites of Thar­sis Montes, the three aligned vol­ca­noes left of cen­tre and Olym­pus Mons, above and left. This ‘grav­ity’ map will help fu­ture craft chart their or­bit with greater pre­ci­sion.

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