General Meeting Report,
13 June at the National Herbarium.
Water On Mars
Speaker Dr Nick Hoffman
In his easy-going, matter-of-fact manner Dr Nick Hoffman from Latrobe University started by announcing tonight’s presentation on Mars was going to be a play in three acts. Not a drama, but a comedy, because of a series of misconceptions that had bedevilled the exploration of Mars and turned it into a comedy of astronomical errors.
Act one starts in the year 1870 with Schiaparelli, and Percival Lowell’s interpretation of canali as canals. If there were canals there must be liquid water, and water means life. What’s more, intelligent life to construct networks of canals. Mars was a greening oasis, except for the occasional global dust storm. Science fiction books of the time, like H. G. Wells’ “War of the Worlds” in 1898, very much cultivated this image.
Act two starts in 1964 with the first flybys of the Mariner spacecrafts. It revealed a barren, moonlike surface littered with craters, crevasses and channels, but no canals! In a flurry of new postulates life on Mars went underground into survival mode. Despite all the signs of water erosion on the surface, there was no actual water to be found. An atmosphere of almost pure CO2, and no H2O. The lack of bleaching in some of the surface features put paid also to the suggestion these features were caused much earlier when surface water was plentiful. Mike Malin and Ken Edgett stunned the Mars research community with images of young flow features on Mars. A very large number of gullies show signs of fluid flow down channels in the centre, leading to deposits at the foot of slopes. The comedy has now turned into a mystery and act two closes with a shot of little Rover in a barren landscape standing silently and dumb-founded in front of a big bolder.
Act three opens in the year 2000, and with a physics lesson on the properties of water and carbon dioxide. Did you know that you can not throw snowballs in the antarctic? Snow has to be wet and warm enough to melt under the pressure of your hands, otherwise it will remain a powder and wont form a ball. Carbon dioxide also behaves differently under varying temperature and density conditions. Frozen carbon dioxide (so called dry ice) "boils" before it melts – a process called sublimation (a solid passing directly to a gas) – at -78 C on earth, and in Mars thinner atmosphere at -130 C). Recognising the explosive degassing of liquid CO2 emerging from the subsurface, Nick drew analogies between a chaos zone and the throat of a degassing volcano on Earth. Under high pressure in the ground, CO2 will expand explosively when warmed by the sun and can turn whole mountain sides into so-called density flows that can travel downhill at speeds up to 500km per hour. The sudden release of pressure and internal friction will vaporise the remaining CO2 and keep the momentum going all the way down. That is how the “flow” channels are carved out of the Martian surface!
“White Mars” Nick calls this theory and the project he developed around it. The idea for the title came to him from a fictional trilogy by Kim Stanley Robinson, Red Mars / Green Mars / Blue Mars, that deals with possible future terraforming of Mars. The naming convention was so evocative that the new "iceworld Mars" concept became "White Mars".
While most researchers are not yet prepared to adopt a model as extreme as White Mars, aspects of it are being incorporated into most serious studies of flow processes and surface conditions on Mars. Within the next few years, the question on Mars may no longer be "How warm and wet?" but "How cold and dry?" Indeed, the fundamental question of White Mars is "Do any features on the planet actually require liquid water, or can we use CO2 for everything?" For those who persist in saying that if it walks like a duck and has a beak like a duck, then it must be a duck, perhaps they should read up about the platypus. These marsupials even lay eggs but they don't quack!
For further reading on this fascinating subject and all its implications you can visit Dr. Nick Hoffman’s excellent web-page “White Mars”. Just ask your search engine to look for that name and it will take you straight to Latrobe University’s Nick Hoffman.