Planet mars is the fourth planet from the sun and sits next to our planet. That distance is very promising in search for life with ease. From the current explorations, reasons for life could and couldn't thrive on mars.
Presence of liquid water: we know that moisture can help in metabolism of organisms. However, liquid water in mars is not so much but has created a way to make it happen.
Temperature: The temperature of mars can support life. Disregarding the super cooled polar caps (-143C), mars can have a temperature that can help organisms to thrive (from 0-27 C) in some areas.
Ultraviolet radiation: UV rays are greater because of thinner atmosphere. Consequently, this can kill all organisms that are in the surface.
Atmosphere: Mars cannot extensively support life since it has a weak and thin atmosphere. Oxygen are few though Carbon dioxide is abundant.