Methane under the surface of Mars could have warmed up the Red Planet in intermittent bursts, a new study suggests, which could help explain how Mars was warmer and wetter in its ancient past.
Lakes, rivers, and streams flowed across Mars in its first billion years, though today the atmosphere is too thin for these processes to occur. Geologic features show the evidence from orbit, and several NASA rovers have identified many sites where rocks formed in water on the surface. One of Mars’ enduring mysteries is why it is so arid today, yet was so wet so long ago.
Lakes likely endured on Mars for at least several thousand years in a period starting about 3.6 billion years ago, according to the new study, which was published in the journal Nature Geoscience and led by Edwin Kite, an assistant planetary science professor at the University of Chicago.
“But the lake watersheds’ little-weathered soils indicate a largely dry climate history, with intermittent runoff events,” says the study’s abstract. “Here we show that these observational constraints, although inconsistent with many previously proposed triggers for lake-forming climates, are consistent with a methane burst scenario.”
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The methane bursts are linked to obliquity, the tilt of Mars’ axis. The obliquity of Earth is stabilized by our planet’s large moon, but Mars only has two tiny, asteroid-sized moons — leading to wild swings in its axis over millennia. As the obliquity shifts, this also affects temperatures on Mars and the buildup of ice, all of which can destabilize methane clathrate (a compound where a crystal structure of one substance traps molecules of another substance).
The authors ran numerical situations and found “that outgassed methane can build up to atmospheric levels sufficient for lake-forming climates,” because the methane would raise the temperatures of the planet by several degrees. But the methane would have been destroyed in the atmosphere through exposure to sunlight, which would have reduced the duration of lake-forming climates to only a million years.
Methane may not be the only reason behind Mars’ warmer climate. Another line of evidence concerns the Martian atmosphere, which was likely thicker in the ancient past. The atmosphere’s lighter molecules, unprotected from the sun since Mars has no global magnetic field, were pushed into space over time, lessening its overall volume. NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft is studying atmospheric loss today, to better understand the process.
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The methane study comes just weeks after a separate study, published in the GSA Bulletin, found “spectacular” river deposits in the Aeolis Dorsa region of Mars from about 3.5 billion years ago. A statement from the Geological Society of America described them as “some of the most spectacular and densely packed river deposits seen on Mars.”
The river study was led by Benjamin Cardenas, a geosciences Ph.D. candidate at the University of Texas at Austin. His supervisor, professor David Mohrig, is a co-author on the paper.
Satellite images revealed the region’s featured by using a process called topographic inversion, showing how deposits filled up the river channels over time and became easily observable ridges.
The researchers found evidence of river deposits as well as temporal changes in the coastline and how the sediment was built up. The work suggests that a large water body influenced the rise and fall of water levels throughout the valley. Each water level change was likely well over 50 meters (164 feet), similar to historical changes in global sea level on Earth.
“The conclusion that such large water level fluctuations and coastline movements were recorded by these river deposits suggests some long-term stability in the controlling, downstream water body, which would not be expected from catastrophic hydrologic events,” the statement said.