section_path: Other celestial bodies/Mars
section_name: Mars
paragraph_text: Mars
  
  Mars is considerably smaller than Earth and Venus, and there is evidence for ice on its surface and in its crust.
  
  In the 1990s, it was proposed that Martian Crustal Dichotomy was created by plate tectonic processes. Scientists have since determined that it was created either by upwelling within the Martian mantle that thickened the crust of the Southern Highlands and formed Tharsis or by a giant impact that excavated the Northern Lowlands.
  
  Valles Marineris may be a tectonic boundary.
  
  Observations made of the magnetic field of Mars by the Mars Global Surveyor spacecraft in 1999 showed patterns of magnetic striping discovered on this planet. Some scientists interpreted these as requiring plate tectonic processes, such as seafloor spreading. However, their data failed a "magnetic reversal test", which is used to see if they were formed by flipping polarities of a global magnetic field.