1. Journey form earth to moon take approximately 1yr. for example India launch it's satellite for mars mission in 5 nov 2012 and reached mars Orbit in 24 sep 2013 this long time lead to some problem:
A). Long time spend in Zero Gravity leading to weakness of muscles including heart muscles also which was increase the risk of heart attack.
B). It also lead to the weakness of Eyes which was known as stress graft syndrome.
2. In the Mars extreme weather condition in a night time temperature around -153°C and day time around 20 degree Celsius where human do not sustain and technology for it is very costly.
3. Mars atmosphere is thin and It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%).Without a pressure suit, low atmospheric pressure would cause human blood to boil.
4.Lacking a magnetic field, the surface is bombarded with high-energy cosmic rays, requiring radiation shielding for any long-term habitation.
5. Mars Gravity it very less around 38% of earth and exists of iron oxide highly reactive dust—often described as nanophase iron oxides—which poses a significant health hazard if inhaled, ingested, or brought into human habitats.
6.No liquid water exists on the surface now, there are huge, permanent polar ice caps made of water and carbon dioxide, and potentially more water frozen in sub-surface ice
7.Future astronauts will face extreme isolation, confinement, and the "Earth-out-of-view" phenomenon, which will challenge the human psyche.
8. There are some also a morality issue vehicle do not carry all the people of the earth and what happened with the remaining person who has not going to the mars ,it's unfair
why We do not try to maintain earth in human condition rather thanmake it inhabitiual ?