Which is not to say that earlier findings of methane plumes in the planet's atmosphere, made by Mars orbiters and infrared telescopes on Earth, were wrong.
NEWS: Mars Methane Mystery: What's Making the Gas?
Rather, the measurements from Curiosity, taken over an eight-month period, add a new twist into an already intriguing mystery.
"The plumes were already hard to explain before they disappeared," Webster said. "Suddenly, the whole interpretation of the earlier observations is stuck."
On Earth, methane lasts 300 years in the atmosphere before it is broken down by ultraviolet rays from the sun. Taking into account Mars' greater distance from the sun and reduced atmospheric pressure, a plume of methane measured in 2003 should have been an easy find for Curiosity's tunable laser spectrometer.
The instrument shoots infrared beams at air samples and measures how much energy is absorbed at particular wavelengths, a process that reveals concentrations of methane, carbon dioxide, water vapor, and isotopic variations of these gases.