A team of enthusiastic scientists are dressing in space suits and recreating life on Mars – in a rocky red desert on Earth. Current NASA plans include sending humans to the red planet as early as the 2030s. Should we ever establish colonies on Mars, we’d need to build power generation engines.
Now, in research published in the journal Nature Communications, my colleagues and I have found a way to make this happen using a substance easily found on the planet: the solid form of carbon dioxide, known as dry ice.
To understand why, let’s go back to Earth for a moment. Here, we use water to turn the energy stored in coal, oil or gas into useful mechanical or electrical energy through what is known as a “heat engine”. In a steam engine, the most common form of heat engine, fuel is used to heat up water which then vaporizes into high-pressure steam. This steam then powers a turbine to generate electricity, or a locomotive engine to create motion.
This whole situation changes dramatically on Mars; although water is still available on the surface of the red planet, it is locked in solid form. Heating it to melting point and then to boiling point to use it as a working substance requires a lot of energy.
However Martian dry ice already exists close to its “sublimation point” — the temperature at which it turns directly from solid to gas. It therefore only takes a relatively small nudge for dry ice to change states. The challenge is to harness the energy released by this change to power a heat engine — or even a whole colony.
We turned to a common scientific effect you’ve probably noticed before in your kitchen. When a water droplet is placed on a hot surface held above 100° C it boils off, creating steam. However when the surface is heated above a certain temperature, known as the Leidenfrost point, the water no longer boils away. Instead, the drop sits on a layer of its own vapor and levitates on top of the surface. This is known as the Leidenfrost effect.
In a series of experiments, we have shown that carbon dioxide is a viable working substance for heat engines. By channelling the vapor released upon sublimation of dry ice discs on top of turbine-like surfaces, we have been able to use dry ice to power an electrical generator.
Crucially, the vapor produced by the dry ice discs generates enough pressure to overcome gravity, lifting the disc off the turbine surface through the Leidenfrost effect. The discs thus become levitating rotors, meaning the engine is extremely low-friction. Read more…