Filtered light reveals the composition of Martian rocks.
The Curiosity Mars rover looks at a lot of rocks. Most of them are covered in the red planet’s characteristic red dust, which makes it hard to see what they are made of, and even without the dust it can be hard to tell one mineral from another by visual inspection.
The plucky robot doesn’t let that stop it, however. Curiosity has a purpose-built Dust Removal Tool (essentially a wire-bristled brush) to scrub clean pieces of rock for a better look, and its camera has special filters that can make some minerals stand out from others in sharp relief.
The false-colour image above is a composite of shots taken through three filters chosen to make haematite stand out in a vivid shade of purple. An initial inspection of the rock showed little sign of the iron-oxide mineral, but after scrubbing clean a small area about 6 centimetres across Curiosity spotted an unmistakable glimpse of haematite.
The photo was taken on September 17, 2017, during the 1819th Martian day (or sol) of the rover’s mission.