Mars once had earth-like conditions with water and an atmosphere. At some point, however, the atmosphere escaped into space and the water froze. They think it’s because the core of Mars solidified, causing its magnetic field to fail, and the solar wind did the rest. But it was also hit by a big asteroid. The Hellas impact basin is the 2nd largest in the solar system.
The loss of Mars’ atmosphere was probably multifactorial, including the fact that Mars has a lot less mass than Earth, and therefore the escape velocity of atmospheric gases is less. It’s actually very interesting. Look up Atmospheric escape.
Got it. Thanks.