Mars Water, Weather and Climate

Tuesday 18th June, 2019

Our speaker for the evening was Prof Stephen Lewis from the Open University's School of Physical Sciences who came to talk to us about "Mars: Water, Weather and Climate". He said that he has been studying Mars for about 27 years, ever since the Mars Observer spacecraft mission, which launched back in September 1992. Sadly, the mission was not a success as contact was lost with the spacecraft on its way to Mars.

Prof Lewis then mentioned that he was the leading academic consultant on the BBC's new series "The Planets", narrated by Prof Brian Cox. He said that a beach on southern Iceland was used for many of the backgrounds and, although there are many computer-generated images included in the series, a lot of the images are real.

He then continued by saying that in some ways Mars is similar to Earth, in that its day length is only about 37 minutes longer, it has seasons, its axial tilt is currently similar, and it has ice caps at its poles. It also has high and low pressure weather systems that are of a similar scale to that on Earth despite Mars being a much smaller planet. However, there are significant differences, as it has a thin atmosphere of carbon dioxide, no global magnetic field, and a distinct north-south divide to its geographic features. The northern areas of Mars are young lowlands where once there were oceans and in the south there are ancient highland areas.

Prof Lewis explained that, just like Earth, Mars' geological history is divided into periods beginning with the Noachian 4 billion years ago. Orbiting spacecraft have discovered ancient river channels and robotic rovers have found sedimentary layers leading scientists to conclude that large oceans were present in the northern lowland areas in this time period. This is in stark contrast to Earth which was at that time in its Hadean period when most of the surface would have been molten. So, whilst large amounts of water would have made the development of life more likely on Mars, Earth would have been inhospitable.

However, after this period Mars and Earth took very different paths. Roughly 3.75 billion years ago, during the Hesperian period, Mars lost its global magnetic field. With its protective shield gone the solar wind then stripped its atmosphere and the water was either lost to space or froze as surface temperatures plummeted. During the Hesperian period the only time liquid water briefly reappeared was when volcanic activity melted the subsurface frozen water.

The current geologic period for Mars, and its longest, began about 3 billion years ago and is known as the Amazonian. Using computer models, Prof Lewis said that he can predict the weather on Mars up to 30 days in advance, apart from the sudden appearance of dust storms, which can grow to encompass the whole planet in a matter of weeks. He added that the dust on Mars is more like smoke particles than sand and often marks the edge of weather fronts.

Prof Lewis concluded his talk by saying that he already has a weather forecast for the next ExoMars rover named "Rosalind Franklin", which is scheduled to land on Mars in March 2021. He hopes his forecast will match the success he had in predicting the atmospheric conditions when NASA's Curiosity rover touched down on Mars — his prediction was within 1% of the conditions.