New research from the Hubble Space Telescope and NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission shows that Mars loses water faster when it is closest to the sun. These seasonal changes are related to Mars’ orbit, and increased solar heating during perihelion speeds up the escape of hydrogen atoms from the Martian atmosphere. More than three billion years ago, Mars was warm and rich in water, but today it has lost most of its water and has become a dry, inhospitable world.
Effect of season on water loss
John Clarke of Boston University said that there are two main ways that water can be lost on Mars: freezing in the ground or breaking down into atoms and escaping into space. Mars still retains some water in underground reservoirs and ice caps, but most of it has been lost over time. During the Martian summer, water vapor rises to the upper atmosphere, where solar radiation breaks apart water molecules. The hydrogen atoms then escape into space with the solar wind.
New Observations from Hubble and MAVEN
The Hubble-MAVEN collaboration showed that the rate of hydrogen escape is highest during Mars’ perihelion, when the planet is closest to the Sun. During this time, dust storms heat the atmosphere, accelerating water loss. MAVEN data show that the hydrogen escape rate at perihelion is 10 to 100 times higher than at Mars’ farthest point from the Sun (aphelion). The instruments detected that Mars has lost enough water over its history to form a global ocean hundreds of kilometers deep.
The new understanding of water loss on Mars provides important insights into the evolution of the planet and the possibility that it may have supported life in the past.
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