Seán Doran/Laura Martínez/CNET

Curiosity, NASA's Mars rover, has had a busy weekend. After detecting the highest levels of methane yet seen on Mars last weekend, NASA put a pause on the rover's other science activities to follow up on the discovery. On Monday, data from Curiosity's subsequent experiment filtered back to NASA and the spike in methane levels had disappeared, dropping to background levels.

"A plume came and a plume went," said Paul Mahaffy, principal investigator overseeing Curiosity's Sample Analysis at Mars (SAM) instrument, during a NASA town hall event at the Astrobiology Science Conference on Monday. "We're very confident of the measurement."

As the news of Curiosity's startling finding broke over the weekend, many suggested the high methane could hint at the possibility of life on Mars. Methane is an important molecule on Earth and many living organisms excrete it, including microbes.

Mahaffy explained that Curiosity had detected an unusually high level of methane last Wednesday during a routine experiment which tests the concentration of molecules in the atmosphere. The data came back on Thursday and showed a methane level of 21 parts per billion -- around three times higher than had ever been seen before. Thus, Curiosity's weekend plans were scrapped to run the experiment again.

"The methane plume went away ... it's back down now to below 1 part per billion," Mahaffy said, noting the measurement is consistent with what has previously been seen on Mars. NASA cautioned as the news broke over the weekend that the methane detection appears to be from a "transient plume" and Curiosity is not outfitted with the appropriate instruments to tell us whether the plume is biological or geological in origin.

What does that mean for life on Mars? Well, not a lot. Although the original finding was confirmed, we're no closer to discovering its source right now -- that will be up to some of the spacecraft orbiting the Red Planet and future Mars missions. Moreover, the methane spike is certainly an unusual phenomenon but it has been seen by scientists before.

"The methane mystery continues," said Ashwin Vasavada, Curiosity's project scientist at NASA, in a statement. "We're more motivated than ever to keep measuring and put our brains together to figure out how methane behaves in the Martian atmosphere."