What is making methane on Mars?

摘要

The first hard evidence that methane exists on Mars is forcing scientists to confront a crucial question: is it inorganic in origin or a sign that Martian microbes are at work? Methane is broken down by sunlight within a few hundred years on Mars, so whatever process is creating it must be active today. The discovery of the gas, which occurs mostly in patches above icy ground, is arousing interest because on Earth almost all methane comes from living things, ranging from rotting plants to flatulent cattle.