Mounds at a site in the northern plains of Mars bear a striking resemblance to mud volcanoes on Earth (Image: University of Arizona/JPL/NASA)

IS LIFE bubbling onto the Martian surface in muddy squirts? The discovery of what could be mud volcanoes on the planet suggest it is possible, providing a new focus in the hunt for alien microbes.

Three plumes have recently been identified as sources of methane in Mars’s atmosphere (New Scientist, 24 January, p 19). This has led to suggestions that the gas could have been produced by microbes living a few kilometres beneath the surface, where …