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In late May 2019, a spiral-shaped dust storm at the north polar ice cap of Mars was observed by several instruments on board Mars Express. This image was acquired by the High Resolution Stereo Camera on 26 May and covers an area of approximately 2000 by 5000 kilometres.

The spiral shape of the storm arises from the deflection of air masses due to the rotation of the planet, a phenomenon known as the Coriolis force. This effect is also observed on Earth where low-pressure areas at the northern hemisphere – cyclones, for example – have a counterclockwise spiral shape. Storms on Mars are generally weaker than storms on Earth however, because of the Red Planet’s much lower atmospheric pressure – less than one percent of Earth’s atmospheric pressure at the surface – and have less than half the typical wind speeds of hurricanes on Earth.

The swirling pattern of the north polar ice cap can also be seen at the far top-right of the image. At the same time, wispy clouds can be seen along the edge of the ice cap, and also further south (left), around the large volcanoes. The dark patches are dune fields composed of dust-blown volcanic material on the surface that built a giant erg around the polar cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

Between late May and early June, several different irregular and spiral-shaped dust storms were seen to be forming at the north polar ice cap on Mars.

The images shown here were acquired by the High Resolution Stereo Camera on board ESA’s Mars Express spacecraft from an altitude of approximately 10,000 kilometres. The long image strips cover an area of about 2000 by 5000 kilometres, extending from the north pole equatorward to the large volcanoes Olympus Mons and Elysium Mons.

The montage of images shows three different storms developing on 22 May, 26 May, and 6 June. In the latter case, the cameras watched the storm evolve until 10 June, as it moved southward towards the volcanoes.

Thin patches of light-coloured clouds can be seen at the outer margin of the polar cap and also several thousand kilometres away, close to the Elysium volcanoes. At the same time, wispy clouds can be seen along the edge of the ice cap, and also further south (left), around the large volcanoes. The dark patches are dune fields composed of dust-blown volcanic material on the surface that built a giant erg around the polar cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

A dust storm underway at the edge of the north polar ice cap of Mars. The image was acquired by the Mars Express Visual Monitoring Camera on 29 May 2019.

Credit: ESA/GCP/UPV/EHU Bilbao.

This image was acquired with the DLR-operated HRSC stereo camera on 22 May 2019 and shows a dust storm on the edge of Mars' north polar ice cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

This image was acquired with the DLR-operated HRSC stereo camera on 22 May 2019 and shows a dust storm on the edge of Mars' north polar ice cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

This image was acquired with the DLR-operated HRSC stereo camera on 22 May 2019 and shows a dust storm on the edge of Mars' north polar ice cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

This image was acquired with the DLR-operated HRSC stereo camera on 22 May 2019 and shows a dust storm on the edge of Mars' north polar ice cap.

Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.