New research from the Hubble Space Telescope and NASA‘s Mars Atmosphere and Volatile Evolution (MAVEN) mission reveals that Mars sheds water more quickly when it is closest to the Sun. These seasonal changes are tied to the planet’s orbit, where the increased solar heating during perihelion accelerates the escape of hydrogen atoms from Mars’ atmosphere. Over three billion years ago, Mars was warm and rich in water, but today, it has lost most of its water, transforming into a dry, desolate world.

Seasonal Effects on Water Loss

According to John Clarke from Boston University, Mars loses water in two main ways: freezing into the ground or breaking into atoms and escaping into space. The planet still retains some water in its underground reservoirs and ice caps, but much of it has been lost over time. During the Martian summer, water vapour rises into the upper atmosphere, where solar radiation splits water molecules. The hydrogen atoms then escape into space, carried by the solar wind.

Hubble and MAVEN’s New Observations

The collaboration between Hubble and MAVEN has shown that the hydrogen escape rate is highest during perihelion when Mars is closest to the Sun. During this time, dust storms heat the atmosphere, accelerating water loss. MAVEN’s data reveals that hydrogen escape rates are 10 to 100 times higher at perihelion than at the planet’s farthest point from the Sun, called aphelion. The instruments have detected that Mars has lost enough water over its history to form a global ocean up to hundreds of kilometres deep.

This new understanding of Mars’ water loss provides crucial insight into the planet’s evolution and its potential for past life.