Something familiar has been spotted on Mars. The fourth planet from the Sun has an atmosphere that is 95 percent carbon dioxide; this makes it very cold and dry, a complete opposite to the nitrogen and oxygen that make up Earth’s warm wet atmosphere. Despite their differences, the European Space Agency (ESA) thinks that both Mars and Earth have similar cloud patterns, suggesting that they were formed in the same way.
ESA’s Mars Express and NASA’s Reconnaissance Orbiter recorded two dust storms that happened near Mars’s North Pole in the spring of 2019. Springtime is a period of high dust storm activity on Mars. The Visual Monitoring Camera (VMC) images show that the storms occur and disappear in repeated cycles, sometimes showing common shapes. By using the High Resolution Stereo Camera spiral shapes can be seen, which are between 100 and 2,000 kilometers (62-1,243 miles) long, and they bear a similar origin to that of the extratropical cyclones that can be seen at Earth’s mid and polar latitudes.
“When thinking of a Mars-like atmosphere on Earth, one might easily think of a dry desert or polar region. It is quite unexpected then, that through tracking the chaotic movement of dust storms, that parallels can be drawn with the processes that occur in Earth’s moist, hot, and decidedly very un-Mars-like tropical regions,” comments Colin Wilson, ESA’s Mars Express project scientist, in a statement.
The images also reveal that the texture of the clouds on Mars is similar to that of the clouds on Earth. The Martian dust storms are made up of lots of regularly-spaced smaller cloud cells, arranged like pebbles. This texture is formed by closed-cell convection when the warmer air rises in the center of smaller cloud pockets. As on Earth, this warmer air forms the clouds, but on Mars the rising air contains dust, not water. The Sun heats the rising dusty air, forming cells that are surrounded by sinking air that is less dust-laden. This gives rise to the pattern that you see.
By measuring the shadows of the dust clouds, and combining this with the Sun’s position, it is possible to measure the height of the clouds above the surface of Mars. Researchers have found that the dust can reach approximately 6-11 kilometers (4-7 miles) above the ground.
“Despite the unpredictable behavior of dust storms on Mars and the strong wind gusts that accompany them, we have seen that within their complexity, organized structures such as fronts and cellular convection patterns can emerge," explains Agustín Sánchez-Levaga from the Universidad del País Vasco UPV/EHU (Spain), who leads the VMC science team and is lead author of the paper presenting the new analysis.
Monitoring dust storms on Mars is vital for helping solar-powered missions such as InSight survive on the Red Planet and learn as much about Mars as possible.
The paper is published in Icarus.