“The discovery of abundant siderite in Gale Crater represents both a surprising and important breakthrough in our understanding of the geologic and atmospheric evolution of Mars,” Benjamin Tutolo, associate professor at the University of Calgary, Canada, and lead author of the paper, said in a statement.

A NASA rover taking rock samples on Mars has uncovered a plentiful mineral that was invisible to orbiters studying the Red Planet from space.

NASA's Curiosity rover has found iron-rich carbonates on Mars — a major clue that the Red Planet used to be habitable.