Scientist offers a few theories for presence of gas exuded by life forms. Mars scientists in Europe and the United States have detected tantalizing signs of methane gas in the Martian atmosphere, and cannot yet explain why it’s there.

Arid, stony Mars, whose sinuous canyons and broad flood plains have long beckoned Earth-bound explorers, may never have been the warm, wet home of life that scientists have envisioned so hopefully, a new study of the planet’s past maintains. In a scenario that contradicts decades of hints from orbiting spacecraft that rivers and an ocean once covered the Martian surface during a prolonged warm period, scientists at the University of Colorado and NASA’s Ames Research Center are posing a vastly different concept.