ESA’s Mars Express has revealed that Mars is surprisingly producing Earth-like cloud patterns reminiscent of those found in our planet’s equatorial regions.
Earth and Mars have two very different atmospheres. Mars’ dry and cold atmosphere is composed almost entirely of carbon dioxide while Earth’s atmosphere is rich in nitrogen and oxygen. The density of its atmosphere is less than one fiftieth of that of Earth’s – equivalent to the density found at an altitude of about 35 km above the Earth’s surface.
Although they differ greatly, their cloud patterns have been found to be surprisingly Earth-like, indicating similar formation processes.
A new study delves deeper into two dust storms that occurred near Mars’ north pole in 2019. The storms were observed during the Arctic spring, which is when local storms usually form around the retreating ice cap.
Two cameras aboard Mars Express — the Visual Monitoring Camera (VMC) and the High-Resolution Stereo Camera (HRSC) — along with the MARCI camera aboard NASA’s Mars Reconnaissance Orbiter, have imaged the storms from orbit.
The VMC image sequence shows that the storms appear to grow and disappear in repeating cycles over days, showing common features and shapes. Spirals are most notably visible in the wider views of the HRSC images. The spirals have a length of between 1,000 and 2,000 kilometers, and their origin is the same as that of the extratropical cyclones observed in the middle and polar latitudes of the Earth.
The images reveal a specific phenomenon on Mars. They show that Martian dust storms consist of small, regularly spaced cloud cells, arranged like grains or pebbles. Texture also appears in clouds in Earth’s atmosphere.
Familiar textures are formed by convection, in which hot air rises because it is less dense than the cooler air around it. The type of convection observed here is called closed-cell convection, when air rises in the center of pockets or small cloud cells. The gaps in the sky around cloud cells are passages for cold air to sink beneath the rising hot air.
On Earth, the rising air contains water that condenses to form clouds. The dust clouds imaged by the Mars Express show the same process, but on Mars the rising plumes of air contain dust instead of water. The sun heats the dust-laden air causing it to rise and form dusty cells. The cells are surrounded by areas of submerged air with less dust. This gives rise to the granular pattern, which is also seen as clouds on Earth.
By tracking the movement of cells in the image sequence, the Wind speed can measure. Winds blow on the cloud at speeds of up to 140 km/h, causing the cells to elongate in the direction of the wind. Despite the chaotic and dynamic atmosphere of Mars and Earth, nature creates these orderly patterns.
“When thinking of a Mars-like atmosphere on Earth, one might easily think of a dry desert or a polar region. It is quite unexpected, then, that by tracing the chaotic movement of dust storms, parallels can be drawn with the processes that occur,” says Colin Wilson, Mars project scientist. Express by the European Space Agency, ESA, in the hot, humid equatorial regions that aren’t quite like Mars.
One of the main ideas achieved with the VMC images is measuring the height of dust clouds. The length of the shadows they cast is measured and combined with knowledge of the sun’s position to measure the height of the clouds above the surface of Mars. The results revealed that the dust can reach approximately 6-11 km above the Earth’s surface and the cells have typical horizontal sizes of 20-40 km.
“Despite the unpredictable behavior of dust storms on Mars and the strong winds that accompany them, we have seen that, given their complexity, structured structures such as fronts and cellular convection patterns can emerge,” explains Agustín Sánchez-Levaga from Universidade del Pais. Vasco UPV/EHU (Spain), who leads the VMC science team and lead author of a paper presenting the new analysis.
Such an organized cellular load is not unique to Earth and Mars; Arguably, observations of Venus by Venus Express show similar patterns. Agustín adds: “Our work on Mars’ dry convection is another example of the value of comparative studies of similar phenomena occurring in planetary atmospheres in order to better understand the mechanisms behind them under different conditions and environments.”
And also learn more about how to do this Planetary atmospheres “Working,” understanding dust storms is relevant to future missions to Mars. In extreme cases, dust storms can block much sunlight from reaching the rover’s solar cells on the Red Planet’s surface. In 2018, a planet-wide dust storm not only blocked sunlight from reaching the surface, but also covered the solar panels of NASA’s Opportunity spacecraft in dust. These two factors cause the rover to lose electrical power, ending the mission.
Monitoring the development of dust storms is critical to help protect future solar-powered missions – and eventually manned missions to the planet – from such powerful phenomena.
Cellular patterns and dry load textured Sand Storms At the Edge of Mars North Polar Cap, by A. Sánchez-Lavega et al, published in the November 15, 2022 issue of the Journal Icarus.
A. Sánchez-Lavega et al, Cytotypes and Dry Convection in Dust Storms at the Mars North Polar Cap Rim, Icarus (2022). DOI: 10.1016/j.icarus.2022.115183
European Space Agency
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