86331
Mariner 9 in 1972 discovered a belt of sand dunes that ring the polar ice deposits , which is 500 km across in some places and may be the largest dune field in the solar system .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities:  
Answer:
 None