Lindsay Lecture

Living systems produce more than 90% of Earth's atmospheric methane; the balance is of geochemical origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes associated with discrete active regions. In Northern mid-summer, the principal plume contained ~19,000 metric tons of methane, and the estimated source strength (≥ 0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California. By vernal equinox about one-half the released methane had been lost. Its possible origins will be discussed in the context of geologic and biologic terrestrial analogues.