The theory of ancient life on Mars is gaining strength. Studies have proved that the planet had right conditions for the formation of RNA (ribonucleic acid) molecules. It also had water in liquid form long time ago. Then life must have formed on Mars consistent with the RNA.
Our capabilities are limited by the distance and technology to find strong evidence through exploration. Another method is to create the geochemical history of the planet and find out if the planet was hospitable. This was done by a team of researchers led by planetary scientist Angel Mojarro of MIT. Based on this geochemical model, though a well educated guess, we cannot rule out the chance that RNA existed in Mars.
The research is uploaded to the pre-print server bioRxiv and is yet to be peer-reviewed.