CAPE CANAVERAL, July 17 — For the engineers at SpaceX, methane is not just a fuel. It is the key to a future on Mars. The company’s Starship, a fully reusable launch system designed for deep-space travel, runs on liquid methane — a choice driven by the gas’s efficiency, its availability, and the tantalising prospect of making rocket fuel on the red planet itself.
Methane, with the chemical formula CH4, is the simplest alkane and the main component of natural gas. At standard temperature and pressure, it is an odourless, colourless, transparent gas.
That very property — being a gas under ordinary conditions — makes it difficult to capture and store. To use it as a liquid fuel, engineers must keep it at cryogenic temperatures, below its boiling point of -161.5 degrees Celsius at one atmosphere of pressure. That is cold enough to freeze carbon dioxide out of the air.
Handling liquid methane presents real engineering challenges. The cryogenic storage and transfer systems must maintain those extreme temperatures, and they must manage boil-off — the inevitable loss of fuel as it warms and turns back into gas.
SpaceX has spent years developing the tankage and plumbing to keep methane cold and contained through the violent vibrations of launch and the long coast of spaceflight.
Why methane for Mars?
The choice of methane over other fuels comes down to Mars itself. Liquid methane can theoretically be produced on the Martian surface using local resources — a process called in-situ resource utilisation. The Martian atmosphere is mostly carbon dioxide, and combined with water ice found on the planet, it could be processed into methane and oxygen.
That means a Starship could refuel on Mars for the return trip, rather than carrying all its fuel from Earth. Methane is also an economically attractive fuel on Earth because of its abundance.
It is a group-14 hydride and an organic hydrocarbon. It is flammable in air at concentrations between 5.4 and 17 percent. When it burns, it produces carbon dioxide and water.
That clean combustion is part of its appeal for a reusable rocket engine. There is a catch, however.
Partial oxidation of methane to methanol — a potentially useful industrial chemical — is notoriously difficult. The reaction tends to run all the way to carbon dioxide and water, even when oxygen is scarce. Nature has a solution: the enzyme methane monooxygenase can convert methane to methanol, but that biological process is not scalable for industrial use.
A greenhouse gas with a hidden smell
Methane is also a potent greenhouse gas. It is transparent to visible light but absorbs infrared radiation, trapping heat in the atmosphere. That makes it a significant contributor to climate change when it leaks into the air.
The familiar smell of natural gas — that rotten-egg odour that alerts people to a leak — does not come from methane itself. It comes from added odorants, such as tert-butylthiol, which are mixed in for safety.
At very low temperatures, methane takes on a solid form. Under normal pressure, cooling methane produces what is known as methane I, a plastic crystal in the cubic system with the space group Fm3m. In that state, the molecules can still rotate freely, even though they are locked in a crystalline lattice.
Beyond Earth
Methane has been detected on Mars, a finding with implications for astrobiology. Its presence raises questions about whether it is produced by geological processes or by life. For now, that remains an open question.
But for the engineers working on Starship, the practical question is how to handle the stuff reliably, day after day, in the vacuum of space and on the surface of another world. The cryogenic challenges are real.
The boil-off problem is real. But the potential payoff — a fuel you can make on Mars — is what keeps the teams going. The next time a Starship lifts off from Texas, it will be burning methane, and the people who built it will be watching every tank, every valve, every degree of temperature.
Sources
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