Mars’ ancient warmth and the mystery of its missing air

Rocks show that early Mars hosted liquid water, but whether it was warm remains debated. The planetary dynamo likely died between about 4.2 and 3.7 billion years ago, removing the magnetic shield and enabling solar wind to strip gas—an escape process MAVEN measured, especially during solar storms. Some carbon dioxide may have been stored in minerals like siderite, so not all missing air left to space. The balance between atmospheric loss and crustal storage is still uncertain, and better palaeomagnetic dating and additional sampling are needed to pin down Mars’ climate history. The cold desert is settled, but the path to understanding how it happened is ongoing.