Why does Mars have a thinner atmosphere and cooler temperature than Earth?
Due to low surface gravity mars lost its atmosphere i nto space.
It more distant from Sun than earth.So received less solar radiation
Being small planet Mars cooled down faster than earth after its formation.
Although majority of Mars' atmosphere consists of carbon dioxide, it is not under greenhouse effect like Venus is. The distance of Mars from the Sun also plays an important factor of its temperature
The Earth's magnetic field prevents high charged particles from the Sun from hitting the Earth and stripping the atmosphere off (solar wind or coronal mass ejection). As Mars does not have a magnetic field, the solar wind stripped most of Mars' atmosphere. Mars is also further from the Sun than the Earth is, so it is cooler.