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There are subterranean brine rivers on mars so large that they can be seen from orbit. https://www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-wa

• Retric 10y ago
  Not quite. Here is a link that's probably easer to understand. https://science.nasa.gov/science-news/science-at-nasa/2000/ast29jun_1m https://science.nasa.gov/science-news/science-at-nasa/2000/a... We are not looking at underground water in those pictures we are looking at evidence of likely very short term water causing a tiny amount of erosion in just the right situation. However, it's long been known there is actually quite a lot of ice on Mars.