NASA's Spirit rover has discovered an unusual patch of sand in a hollow on its journey to the crater "Bonneville". An unusual pattern of irregular lines and polygons in the soil could indicate the presence of a salty brine. This could mean there's liquid water right below the surface of Mars, which could harbour life - microbes thrive in similar environments on Earth. The rover dug a trench and examined the spot with its array of instruments, which scientists will study intensely back on Earth.