The idea that Mars was once covered in oceans and rivers of liquid water is well established; billions of years ago its surface was home to around the same amount of water as the Atlantic Ocean, thus raising the possibility that it may have once supported primitive forms of extraterrestrial life.
Since then however, Mars lost most of its water, leaving the barren surface we see today.
The prevailing theory is that after the planet lost its protective magnetic field, the majority of the water and atmosphere of Mars was stripped away by the solar wind coming from the Sun.
Most of the water that was lost disappeared between 4.1 billion and 3.7 billion years ago.
“Mars basically became the dry, arid planet we know today 3 billion years ago,” said study lead author Eva Scheller from the California Institute of Technology.
Now however, data from NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) mission as well as the European Space Agency’s Mars Express orbiter has suggested that the amount of water Mars could have lost over the last few billion years was much smaller than previously thought.
Scientists now believe that a significant amount of water could still be there, locked up inside the crystal structures of rocks deep in the planet’s crust.
Just how accessible this remaining water will be to future Mars explorers however remains unclear.