Mars

Environmental Characteristics
Carbon dioxide atmosphere
Abundant sunlight
Very cold environment
Many nutrients in soil
Land/soil and ice both abundantly present

 

Io

Environmental Characteristics
Sulfur dioxide atmosphere
Very cold environment
No water
Abundant light
Volcanically active/possible sulfur lakes

Europa

Environmental Characteristics
Oxygen atmosphere
Very cold environment
Lots of ice present
Water may be present
Limited sunlight

 

Titan

Environmental Characteristics
Methane gas atmosphere
Very cold environment
Lakes/oceans of ethane
May have continents (land)
Abundant light