Today NASA has made the historic announcement that liquid water has been discovered on the surface of Mars. Ice has been found on Mars previously, and evidence has shown that Mars once had large amounts of water that were lost over time, but this is the first time liquid water has been observed on the surface of the planet.
Details of the discovery have been published in a paper in Nature Geoscience, and they focus on the salty water discovered in recurring slope lineae (RSL) under certain seasonal conditions. Scientists have observed RSL in the past, and found that they appear and dissipate in seasonal patterns but could not confirm that they were caused by liquid water until recent observations including those by the orbiting HiRISE instrument on board the Mars Reconnoissance Orbiter.
The presence of water on Mars raises new questions about the possibility of current life on Mars, and could impact how future Mars missions are conducted to answer those questions.
images via NASA/JPL/University of Arizona