It is easy to go to the Mars but the long duration of return journey could kill the immune system of the traveller making his health condition like a patient of Aids, according to a top NASA scientist of Indian origin. It would take three years for a space craft flying at an average speed of 35 thousand kilometre per hour to reach the Mars and during this period the immune system of the traveller could be wrecked, NASA scientist and President of the Centre for Global Studies Professor Saroj Mishra told PTI here yesterday.