Humans cannot currently live on Mars in an unprotected or natural state due to extreme environmental challenges such as toxic soil, very thin carbon dioxide atmosphere, extreme cold, high radiation levels, and lack of breathable oxygen. However, scientists are exploring possible ways to enable human habitation on Mars either temporarily in protected habitats or in the very long term through planetary engineering processes like terraforming to create a thicker, warmer atmosphere with breathable air. Key challenges for living on Mars include:

• The surface is chemically toxic and would be lethal without protection.
• The thin atmosphere provides almost no oxygen and minimal protection from harmful cosmic and solar radiation.
• Mars is very cold, with temperatures much lower than Earth.
• Liquid water is scarce, mostly existing as ice mixed with carbon dioxide ice.
• Growing food would require innovative methods like water or tank farming due to lack of soil and harsh conditions.
• Habitats must provide radiation shielding, temperature control, oxygen supply, and protection against dust storms.

Scientists have also found some microorganisms like cyanobacteria that might survive in simulated Martian conditions, offering hope for biological support systems in human outposts. Although terraforming Mars is considered possible by some climate models, it would require enormous time and resources and is not feasible in the near future. In summary, humans can potentially live on Mars with advanced life-support systems and habitat engineering overcoming the harsh Martian environment, but living freely on Mars requires future technological breakthroughs and possibly planetary transformation that are not yet realized.