Final answer:
Liquid water cannot exist on Mars for very long due to its low temperatures, low pressure, and lack of a magnetic field and ozone layer.
Step-by-step explanation:
Liquid water cannot exist on Mars for very long due to the combination of low temperatures, low pressure, and the absence of a magnetic field and ozone layer. Mars has low temperatures and pressures at the surface, causing water to either freeze or boil away. Additionally, without a magnetic field and ozone layer, the surface of Mars is exposed to harmful solar ultraviolet radiation and energetic particles, making it even more inhospitable for liquid water.