The researchers drew together different lines of evidence collected over a Martian year, and from different instruments carried by the Curiosity rover.The Rover Environmental Monitoring System (REMS) - essentially the vehicle's weather station - measured the relative humidity and temperature at the rover's landing site of Gale Crater.Scientists were also able to estimate the subsurface water content using data from an instrument called Dynamic Albedo of Neutrons (DAN). These data were consistent with water in the soil being bound to perchlorates.Finally, the Sample Analysis at Mars (SAM) instrument gave the researchers the content of water vapour in the atmosphere.The results show conditions were right for the brines to form during winter nights at the Martian equator, where Curiosity landed. But the liquid evaporates during the Martian day when temperatures rise.Javier Martin-Torres, a co-investigator on the Curiosity mission and lead scientist on REMS, told BBC News the detection was indirect but convincing: "What we see are the conditions for the formation of brines on the surface. It's similar to when people were discovering the first exoplanets.