the crust. Detection of the mineral by-product serpentinite would suggest that this process is occurring. An analog on Earth suggests that low-temperature production and exhalation of methane from serpentinized rocks may be possible on Mars. Another possible geophysical source could be ancient methane trapped in clathrate hydrates that may be released occasionally. Under the assumption of a cold early Mars environment, a cryosphere could trap such methane as clathrates in a stable form at depth, which might exhibit sporadic release. On modern Earth, volcanism is a minor source of methane emission, and it is usually accompanied by sulfur dioxide gases. However, several studies of trace gases in the Martian atmosphere have found no evidence for sulfur dioxide in the Martian atmosphere, which makes volcanism on Mars unlikely to be the source of methane. Although geologic sources of methane such as serpentinization are possible, the lack of current volcanism, hydrothermal activity or hotspots is not favorable for geologic methane. It had also been proposed that the methane might be replenished by meteorites entering the atmosphere of Mars, but researchers from the Imperial College London found that the volumes of methane released this way are too low to sustain the measured levels of the gas. It has been suggested that the methane was produced by chemical reactions in meteorites, driven by the intense heat during entry through the atmosphere. Although research published in December 2009 ruled out this possibility, research published in 2012 suggested that a source may be organic compounds on meteorites that are converted to methane by ultraviolet radiation. Lab tests have demonstrated that bursts of methane can be produced when an electrical discharge interacts with water ice and CO2. The discharges from the electrification of dust particles from sand storms and dust devils in contact with permafrost ice may produce about 1.41×1016 molecules of methane per joule of applied energy. Current photochemical models cannot explain the apparent rapid variability of the methane levels on Mars. Research suggests that the implied methane destruction lifetime is as long as ≈ 4 Earth years and as short as ≈ 0.6 Earth years. This unexplained fast destruction rate also suggests a very active replenishing source. A team from the Italian National Institute for Astrophysics suspects that the methane detected by the Curiosity rover may have been released from a nearby area called Medusae Fossae Formation located about 500 km east of Gale crater.