Mars atmosphere is only a few percent of the pressure of Earth's atmosphere. The Earth and Mars have similar surface temperatures at mid-day. Mars' atmosphere is 95% carbon dioxide, and would have an average molecular weight of about 44 AMU (atomic mass units). The Earth's atmosphere is mostly nitrogen with some oxygen, carbon dioxide, and argon. Its average molecular weight is therefore much less, at 28.9 AMU. Also on Mars the mean adiabatic index is about 1.1 compared to 1.4 for air on Earth. Since the speed of sound in dry air at Earth's surface is about 331 m/s, what would you expect the speed of sound to be on Mars? About 240 m/s because of the lower and higher molecular weight of Mars atmosphere. Very low because of Mars low atmospheric pressure The same as on Earth since the temperature is about the same. About 270 m/s because of Earth's atmosphere having less mass per molecule