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While there is water frozen at the Martian poles and evidence of vapour in the atmosphere, this is the first time liquid water has been found on the planet.
The findings are published in the Proceedings of the National Academy of Sciences.
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By measuring how fast seismic waves travel, scientists have worked out what material they are most likely to be moving through.
“These are actually the same techniques we use to prospect for water on Earth, or to look for oil and gas,” explained Prof Michael Manga, from the University of California, Berkeley, who was involved in the research.
The analysis revealed reservoirs of water at depths of about six to 12 miles (10 to 20km) in the Martian crust.
I’m no astroseismologist but I feel like I’ve heard of sensors like this being on satellites like to investigate glaciers etc. though maybe 10km of rock isn’t so easily penetrated.