How to find life on Mars

To convince most scientists, a mission would need to spot physical remnants of life, such as microbial fossils that retain a cellular structure

The first box scientists need to tick in the hunt for alien life is the presence of water. Life as we know it cannot emerge and survive without water, so a planet needs water to be habitable. Mars had lakes and oceans in the distant past, but now only very salty brines flow there.