Sulphur-rich rocks on Mars. Image from NASA's Mars exploration rover Spirit of sulphur-rich rocks in Columbia Hills. A 4.5 centimetre wide hole has been dug into a soft layered rock, named Peace", by the rover's rock abrasion tool. It has exposed sulphur-rich rock (grey). The sulphur content of the rock and its softness are thought to be evidence of past alteration by water. Spirit and its sister rover Opportunity were launched in the summer of 2003. Spirit landed on Mars on 3 January 2004. Its mission is to analyse soil and rocks and search for water. Image taken on Spirit's 381st Martian day, 27 January 2005."