Mars has always held a special place in our hearts, likely from hints over the decades of perhaps finding signs of life, albeit fossilised and primitive. It’s been the subject of study from telescopes and space missions alike, most notably ESA’s Mars Express which has been observing the red planet for 20 years. Over the two decades of observation it has studied an amazing variety of atmospheric phenomenon which have now been catalogued in a new ‘Cloud Atlas.’ Many will be familiar to sky watchers on Earth but some are very different. 

The atmosphere of the red planet is thin and mostly composed of carbon dioxide. There are traces of nitrogen and argon but with an atmospheric pressure of just 1% of the Earth’s it’s inhospitable for human life. The rarefied atmosphere provides insufficient insulation to the surface leading to aggressive temperature fluctuations from -125°C on night time side to 20°C during the day. It’s not unusual for dust storms to whip up in the atmosphere sometimes encircling the entire planet. It’s in this atmosphere that a multitude of cloud features have been observed. 

Over the last 20 years, Mars Express has been studying the cloud formations in the Martian atmosphere. It was launched in June 2003 to study Mars remotely from an orbit around the red planet. Mars Express was not only studying atmospheric phenomenon but also the surface, subsurface and geological history. With a suite of scientific instruments from high resolution cameras and radar to spectrometers and atmospheric sensors, Mars Express is well equipped for the task. 

Using the High Resolution Stereo Camera (HSRC) on board Mars Express, images of a multitude of clouds have been captured. The clouds are usually the result of microscopic dust particles in the atmosphere around which, water and carbon dioxide crystals form. The dust particles themselves can be left hanging in the atmosphere following unusually strong winds that lift large quantities of dust into the atmosphere. They are occasionally seen as large beige coloured clouds. In the north polar regions it’s possible to see giant spiral dust storms as cyclonic storm systems develop. They are one of the drivers of the global weather systems seen on Mars and studying them is crucial to understanding the dynamics of the atmosphere. 

So called ‘gravity waves’ are a common sight on Mars as they are on Earth. Somewhat resembling rolling hills or the rippling of water, they are usually seen in the mid-latitudes in the colder winter months. A particular type of these gravity waves, known as Lee waves, can build up on the downwind side of mountains and ridges. The presence of the mountain or other large obstacle disturbs the laminar flow of air to generate the effect.

The study has led to a Martian cloud spotters dream, the publication of a fully browsable 20-years of cloud images and data. It was created by the German Aerospace Centre (DLR) in Berlin and is proving invaluable helping researchers to gain a better understanding of the Martian atmosphere. In particular how the different dynamical processes can lead to the clouds seen. The ‘Atlas’ which is available to the public here has been presented at the Europlanet Science Congress in Berlin by Daniela Tirsch form DLR.

Source : Cloud Atlas of Mars Showcases Array of Atmospheric Phenomena