Around this locality in the Clay Unit of Gale Crater we have been doing more methane measurements with the SAM instrument. This highlights the enigmatic nature of Mars’ atmospheric methane. A couple of weeks ago we analysed a large spike at 20 parts per billion molecules. Then a few a days to follow this up we returned to background levels at around 1 ppb. This may explain why Trace Gas Orbiter hasn’t yet identified any methane from orbit, it is transitory. Formation of some clay-like phases (in particular serpentine) can release methane, so possibly ancient methane is being periodically released from the Clay Unit. To get further information about biological or non biological origins – particularly isotopes of carbon and hydrogen – will need sample return, starting with the next NASA rover Mars2020.