In what may be a first for peer-reviewed scientific literature, a new report based on an investigation by NASA's Curiosity Mars rover and examined by an astronaut while she was on the International Space Station (ISS) reveals how profoundly different geology on Mars operates from that on Earth. The work is part of an ongoing effort to understand the rock cycle on Mars, that is, how rock strata are generated, changed, and destroyed, which would offer geologists a sort of Rosetta Stone to read and interpret the observations and samples gathered by present and future Mars missions.
The paper's primary result is that the seemingly mild force of wind erosion drives the process that uncovers stratified strata of rock on Mars. This is in sharp contrast to Earth, where rock strata are revealed by a dynamic combination of tectonic action, which moves chunks of land higher, and river water erosion, which slices into those rocks from the top down.
According to John P. Grotzinger, Harold Brown Professor of Geology and Ted and Ginger Jenkins Leadership Chair of the Division of Geological and Planetary Sciences, the wind on Mars behaves like a feather duster over hundreds of millions to billions of years. This is in stark contrast to Earth, where the great roughness of the San Gabriel Mountains is the result of torrents of precipitation slicing the landscape over relatively short periods of geologic time.
Grotzinger is a former Curiosity mission project scientist and co-author of the Mars erosion report, which was published on June 8 in the Journal of Geophysical Research: Planets (JGR). Jessica Watkins, the paper's primary author, worked with Grotzinger as a postdoctoral researcher at Caltech. Watkins was chosen as a NASA astronaut in June 2017, and she will go into space in April 2022 to serve on the International Space Station. Watkins completed the JGR manuscript while still a postdoc at Caltech and submitted it to the journal as she began astronaut training. She was in space by the time the print proofs were available for her to evaluate, so she offered her final comments on the paper from low-Earth orbit.
Consider the Himalayan Mountains in Asia, which are home to Mt. Everest, to understand the variations between landform creation on Earth and on Mars. The mountains are being pushed upward by tectonic forces that are pushing the Indian subcontinent into Asia, yet the Indus River is steadily cutting down through the rising landmass. Both processes expose rock layers, which geologists use to learn more about the planet's evolution and history. Despite the observation of minor marsquakes by the Mars InSight lander, Mars lacks the tectonic plates that drive the majority of Earth's shaking. Instead, eolian, or wind, erosion has sculpted the red planet nearly totally.
Because Mars' air volume is just 1% that of Earth, one may not anticipate wind erosion to be so significant on the planet. Geologists have contended in recent decades that the influence of current wind action to create erosion on Mars is quite minimal. Nonetheless, it now appears that wind erosion plays a crucial role in driving the rock cycle on Mars, at least prior to 3 billion years ago, when the rocks in Gale Crater were produced and then degraded.
Gale Crater is a 96-mile-diameter dry lake located just below Mars' equator. The Murray Formation, a 300-meter-thick layer of stratified mudstone named for the late Bruce Murray, a Caltech professor of planetary science and former head of NASA's Jet Propulsion Laboratory (JPL), was tracked by Curiosity as it drove through it. Mudstone is a kind of rock created by the compression of fine-grained mud over time.
Watkins, Grotzinger, and their colleagues discovered that the Murray formation, which was built from water-deposited sediments, had been eaten away from the top down when studying Curiosity's data. Furthermore, the layers deposited on top show cross-bedding, which is typical of ancient sand dunes traveling across a desert, propelled by the wind. Overall, the area appears to be a moist ecosystem that has been taken over by the Gobi Desert.
According to Grotzinger, Gale Crater is a beautiful location where several cycles of erosion may be documented. All of this helps us understand how Mars functions in general and will help scientists analyze the Perseverance rover's discoveries.
The article is titled Burial and Exhumation of Sedimentary Rocks Revealed by the Base Stimson Erosional Unconformity, Gale Crater, Mars.
Journal Iformation: Jessica A. Watkins et al, Burial and Exhumation of Sedimentary Rocks Revealed by the Base Stimson Erosional Unconformity, Gale Crater, Mars, Journal of Geophysical Research: Planets (2022). DOI: 10.1029/2022JE007293