|View from Curiosity looking south-southwest in Gale Crater|
The first tests for methane performed by Curiosity have come back negative. At least during the rover's first weeks on Mars, any methane present in the air above Gale Crater was at levels lower than five parts-per-billion. But the scientists studying the Martian atmosphere haven't come away disappointed. Detailed measurements of the isotopes present in the first samples indicate that the Martian atmosphere was once much thicker, which may help explain the past existence of liquid water on its surface.
...Good article from John Timmer with the latest details from the Sample Analysis at Mars, or SAM instrument.