How did Mars lose its atmosphere?

Answer 1

The planet Mars is slightly smaller than the Earth and therefore has a weaker gravitational field. Gravity is what holds an atmosphere in place. In a weak gravitational field, an atmosphere will gradually leak away into outer space. That's what happened on Mars.

Answer 2

Mars lost its atmosphere primarily due to the planet's weaker gravity compared to Earth. This led to the escape of gases like carbon dioxide and water vapor into space, along with solar wind erosion. The lack of a strong magnetic field to shield the atmosphere from solar radiation also contributed to its depletion over time.