Mars is known to have an atmosphere but it is very thin as compared to the atmosphere on earth. It is about 100 times thinner as compared to the type of atmosphere that can usually be found on earth. Some say that Mars used to have a thicker atmosphere but because of the solar wind, some of its atmospheres was blown into oblivion.
This explains why the atmosphere that it has now is thin compared to the others. Take note that the atmosphere of Mars is mostly composed of carbon dioxide and it contains almost no trace of oxygen that people need in order to survive.
