Here on earth, carbon dioxide is a pollutant and a greenhouse gas. But thanks to a new engine technology, for colonists on Mars, CO2 could be an easily accessible, native energy source.
The new engine being developed by researchers at Northumbria University in England uses disks of dry ice (solid CO2) and something called the Leidenfrost effect. What is the Leidenfrost Effect? If you've ever flicked drops of water on a skillet to see if it's ready for frying and noticed that the droplets seem to defy gravity as they skitter across the hot surface, you've seen the Leidenfrost effect. When the water droplets come into close proximity with a surface that is much hotter than the water's boiling point, a bubble of water vapor forms between the skillet and the droplets, causing them to levitate.
Dr. Gary Wells, co-author of a paper on the Northumbrian team's new motor, explains how their device takes advantage of this same effect using disks of dry ice: "... the high-pressure vapour layer creates freely rotating rotors whose energy is converted into power without the need of a bearing, thus conferring the new engine with low-friction properties." The lower a device's friction, negligible in the case of a levitating disk of dry ice, the higher its efficiency.
Why might this be important for Martian colonists? Though dry ice does not occur naturally here on Earth, large regions of Mars are much colder, well below carbon dioxide's freezing point. With Mars' mostly carbon dioxide atmosphere, dry ice there is both naturally occurring, (meaning it would not have to be shipped to Mars from Earth), and in huge supply.
Dr. Rodrigo Ledesma-Aguilar, another co-author of the paper on the Northumbrian team's research, explains: "Carbon dioxide plays a similar role on Mars as water does on Earth. It is a widely available resource which undergoes cyclic phase changes under the natural Martian temperature variations." Mars' north pole, which has a diameter of about 620 miles, seasonally develops a layer of dry ice that is about three feet thick. On Mars' south pole, which is about 220 miles across, there is a permanent layer of dry ice layer that is over 26 feet thick. With a system of Leidenfrost-based generators, these polar dry-ice deposits could become the Martian equivalent of Earth's Middle-east oil fields.
"Perhaps future power stations on Mars will exploit such a resource to harvest energy as dry blocks evaporate," Dr. Ledesma-Aguilaror postulates, "to channel the chemical energy extracted from other carbon-based sources, such as methane gas."
"One thing is certain," Ledesma-Aguilaror concludes, "our future on other planets depends on our ability to adapt our knowledge to the constraints imposed by strange worlds, and to devise creative ways to exploit natural resources that do not naturally occur here on Earth."