NASA’s Mars Reconnaissance Orbiter (MRO) launched in 2005 has helped scientists determine that Mars had surface water as recently as 2 billion years ago. Previous studies had concluded that water on Mars evaporated about 3 billion years ago and this new find reduces that timeline significantly.
Now scientists have found signs of liquid water on the Red Planet as recently as 2 billion to 2.5 billion years ago, meaning water flowed there about a billion years longer than previous estimates.
While the shape of certain valley networks hinted that water may have flowed on Mars recently, the salt deposits provide the first mineral evidence confirming the presence of liquid water. The discovery raises new questions about how long microbial life could have survived on Mars, if it ever formed at all. Ellen Leask, post-doctoral researcher at Johns Hopkins University’s Applied Physics Laboratory, along with professor Bethany Ehlmann from California Institute of Technology (Caltech), used data from the MRO instrument called the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to map the chloride salts across the clay-rich highlands of Mars’ southern hemisphere.
These craters were one key to dating the salts: The fewer craters a terrain has, the younger it is. By counting the number of craters on an area of the surface, scientists can estimate its age.
MRO has two cameras that are perfect for this purpose. The Context Camera, with its black-and-white wide-angle lens, helps scientists map the extent of the chlorides. To zoom in, scientists turn to the High-Resolution Imaging Science Experiment (HiRISE) colour camera, allowing them to see details as small as a Mars rover from space.