Mars is universally known as the Red Planet, but a stunning photograph released by US space agency NASA has revealed the complexities of its colour palette.
The striking image was captured by Nasa's Mars Reconnaissance Orbiter's (MRO) camera, which is managed by the University of Arizona, on January 24 and released this week while the planet remains in the grip of a massive sand storm.
The storm has silenced Nasa's solar-powered Opportunity rover but its better-known Curiosity rover has not been affected, continuing to collect data and even posing for a dusty selfie.
The dune was spotted on Mars' Lyot Crater region and researchers suspect it might be made of "finer material" than neighbouring dunes, according to a statement from the space agency.
The MRO image zooms in on the floor of the crater, where a cluster of regular sand dunes is overlaid by one huge blue sand dune, sprawling over the landscape.
The smaller dunes are classic barchan dunes — the technical term for a crescent-shaped dune formed by gusts of wind.
The big blue one, however, "appearing like turquoise blue in enhanced colour, is made of finer material and/or has a different composition than the surrounding," Nasa said.
Planetary Geologist Alfred McEwen, one of the scientists who operates the University of Arizona's High Resolution Imaging Science Experiment (HiRISE) camera that took the photograph, explained how it came to be.
"The images are given min-max stretches in each individual colour image to increase contrast," McEwen told science site Inverse.
"The dunes are actually grey, but appear relatively blue after such a stretch because most of Mars is red."
MRO, which blasted into space in 2005, is studying the history of water on Mars.
Curiosity rover has previously shown that the planet is home to sand dunes the size of football fields, as well as small sand ripples.