Fact	Assumption	Experiment
Life on Earth requires water Water is located near the Martian poles Water is located beneath the Martian surface	-Life will only exist on Mars near water -Look underground or near poles	Drill below the surface and test for water.
-Mars probably has an oxidizing surface due to the presence of superoxides -Mars has very little atmospheric pressure -The atmosphere is mostly CO2 -The surface is unshielded from UV radiation	Martian life, if it exists, will not exist on the surface; rather, it will exist deep underground or below the surface of large rocks	-Examine the surfaces of rocks for evidence of life just below the rock surface -Drill
-Life on Earth is carbon-based -Carbon has by far the most diverse chemistry of any element	Martian life will also be carbon based	Test for the presence of complex organic molecules
Earth life is based on four particular organic compounds: nucleic acids, proteins, carbohydrates, and lipids	Martian life will also use these classes of compounds	Test for the presence of these compounds
Life on Earth is associated with energetic simple molecules	Martian life will also use these energy sources	Look for energetic simple molecules, such as CH4, H2, CO, H2S, and FeS, as well as evidence of past carbon and nitrogen cycles
Life on Earth is attracted to sources of thermal and light energy	The surface is inhospitable, so Martian life will be attracted to geothermal heat sources.	Look for geothermal heat sources [will be done by satellite not part of mission]
-Earth life metabolizes organic molecules -Earth life produces gaseous products of such metabolism	Mars life will also metabolize organic molecules to gaseous products	Look for evidence of metabolic gas products, and confirm that they are not caused by abiotic chemical reactions (labeled-release)
Some forms of Earth life are photosynthetic and chemosynthetic, and able to convert CO and CO2 to complex molecules	There will also be photosynthetic or chemosynthetic Mars life	Look for evidence of CO2 uptake and retention (pyrolytic release)
No Mars missions have examined the subsurface structure of Mars	It would be helpful to have such information in order to drill	Conduct a geological survey
Earth life is occasionally preserved in rocks as visible organic structures	Mars life would be similarly preserved	Examine rocks for visible fossil evidence
Metabolism in Earth life discriminates between different isotopes	Mars life will discriminate similarly	Look for differences in isotope ratios between organic carbon and inorganic carbon