Mars was doomed to desiccation by its small size, a new study suggests.
Thanks to observations by robotic explorers such as NASA’s Curiosity and Perseverance rovers, scientists know that in the ancient past, liquid water coursed across the Martian surface: The Red Planet once hosted lakes, rivers and streams, and possibly even a huge ocean that covered much of its northern hemisphere.
But that surface water was pretty much all gone by about 3.5 billion years ago, lost to space along with much of the Martian atmosphere. This dramatic climate shift occurred after the Red Planet lost its global magnetic field, which had protected Mars’ air from being stripped away by charged particles streaming from the sun, scientists believe.
But this proximate cause was underlain by a more fundamental driver, according to the new study: Mars is just too small to hold onto surface water over the long haul.