The present day habitability of Mars is an area of research that has exploded hugely in the last decade, to the extent that it s often hard to keep track of everything that s going on. This is by way of background material for my other articles on habitability of Mars.
Mars is Earth like in some ways, but in other ways it s very different with its global dust storms every two years, its thick sheets of dry ice at its ice caps in winter. Any fresh water is close to its very low boiling point in the near vacuum. And the eccentric orbit also has a big impact on its seasons.