Uncovering mystery of two-colour dunes in Meridiani Terra region of Mars

Wondering why these Martian dunes have more than one colour?

The sand on Mars is usually dark in colour, as it is usually made up of volcanic rocks like lava flows. The High Resolution Imaging Experiment (HiRISE) - a camera onboard NASA's Mars Reconnaissance Orbiter - operates in long infrared wavelengths that the human eye cannot detect. In HiRISE enhanced color, surfaces like these dune crests appear dark blue to purple. The size of the sand particles is ideal for being moved around by the wind, which over time creates bedforms like these dunes.

HiPOD: Two-Color Dunes in Meridiani TerraWhy are these dunes different colors? Sand on Mars is typically dark in tone, as it commonly derived from volcanic rocks like lava flows. https://t.co/2sSCM67Pi1NASA/JPL-Caltech/UArizona#Mars #science #NASA pic.twitter.com/CR46JQRyEb

— HiRISE: Beautiful Mars (NASA) (@HiRISE) December 27, 2022

According to the HiRISE team, the "tan" or "reddish" surfaces, which are lighter in tone, are made of a different material than the sand-sized particles that make up the majority of these dunes. These smoother, flatter areas of the dunes are covered with a thin layer of global dust. Martian dust is composed of various materials, including oxidized iron, which is similar to rust.

Wind speeds vary with height above the ground, with higher speeds at greater heights and nearly no wind energy at the surface. This is why dust accumulates in flatter dune areas, where the wind energy is not strong enough to remove it, while the higher-lying dune crests, which experience more intense winds, appear dust-free and create the two-color dune effect.

Operated by the University of Arizona, HiRISE is one of six instruments onboard the Mars Reconnaissance Orbiter. The powerful camera has been taking pictures of the Red Planet since 2006 and sending them back to Earth, allowing scientists to study the Martian surface in unprecedented detail.