GRASS GIS has prooven to be a solid system for 
handling and analysis of surface data of features on Earth.
Since GRASS is Free Software, the freedom to use, 
distribute, study and modify it allowed to implement 
it into an efficient working environment for supporting 
planetary science research activities.  The work has been 
focused on the development of procedures to handle reference 
systems used in planetary mapping as well as providing planetary 
bodies' ellipsoidal parameters into GRASS, following
international research institutions conventions and 
recommendations.  The data from planetary science archives 
can then be organized in GRASS maps in their correct 
projection and reference system. 
The practical use of GRASS in planetary mapping is presented
with an analysis of geologic structures of planet Mars, 
using multispectral imagery and topographic data from different NASA 
missions and from ESA's Mars Express.