For years, Mars has been seen as a dry, lifeless planet. But there is growing evidence to suggest this was not always the case. Scientists have already collected evidence suggesting that Mars once had a lot of water. Now, European researchers say they have discovered the first evidence of a huge groundwater system that once existed below the planet’s surface. The European Space Agency, or ESA, says its Mars Express spacecraft helped discover the evidence. It said a new study provides the first geological proof that Mars once had a “planet-wide groundwater system.” The study was a project of researchers from Utrecht University in the Netherlands. Francesco Salese and his team studied images of 24 deep craters in the northern half of the Red Planet. These pictures were captured by ESA’s Mars Express orbiter, which was launched in 2003.