The Sample Analysis at Mars (SAM) tunable laser spectrometer onboard Curiosity last week detected surprisingly high levels of the gas methane at Gale Crater: about 21 parts per billion units by volume (ppbv), the largest amount of methane the rover has ever found.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 1,550 miles (2,500 km) from the surface of the planet. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene shows the entire Valles Marineris canyon system, over 1,240 miles (2,000 km) long and up to 5 miles (8 km) deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 15.5 miles (25 km) high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters. Image credit: NASA / JPL-Caltech.
Curiosity has detected methane many times over the course of the mission.
The rover has also documented how background levels of the gas seem to rise and fall seasonally.
“Curiosity doesn’t have instruments that can definitively say what the source of the methane is, or even if it’s coming from a local source within Gale Crater or elsewhere on the planet,” the Curiosity scientists said.
Curiosity has also noted sudden spikes of methane, but the researchers know very little about how long these transient plumes last or why they’re different from the seasonal patterns.
“With our current measurements, we have no way of telling if the methane source is biology or geology, or even ancient or modern,” said SAM principal investigator Dr. Paul Mahaffy, a scientist at NASA’s Goddard Spaceflight Center.
A selfie taken by NASA’s Mars rover Curiosity on Sol 2291 (January 15, 2019) at the ‘Rock Hall’ drill site, located on Vera Rubin Ridge. Image credit: NASA / JPL-Caltech / MSSS.
After last week’s methane detection, Dr. Mahaffy and members of the SAM team organized a follow-on experiment this past weekend to gather more information.
The results came yesterday: the methane levels have sharply decreased, with less than 1 ppbv detected.
“That’s a value close to the background levels Curiosity sees all the time,” the scientists noted.
The finding suggests last week’s detection was one of the transient methane plumes that have been observed in the past.
“The methane mystery continues,” said Curiosity project scientist Dr. Ashwin Vasavada, from NASA’s Jet Propulsion Laboratory.
“We’re more motivated than ever to keep measuring and put our brains together to figure out how methane behaves in the Martian atmosphere.”
