31 January 2021

Mars has been the subject of fascination for humankind since we were able to look up at the night sky. Early philosophers such as Plato theorized that Mars, and other planetary bodies, had souls because they were “freely” moving through the sky (1). Later, Carl Sagan and other exobiologists during his time were convinced that there was life on the planet, and people’s imagination ran wild (1). However, after the rise of advanced technology, we now know Mars as it is today: a red, dry, most likely lifeless celestial body. Over the years, scientists were constantly absorbed in the question: was there truly life on Mars? The first primitive evidence of life on Mars was made by Dave McKay. McKay made a groundbreaking discovery by studying the minerals on the Mars meteorite ALH84001, which landed on Earth thirteen thousand years ago (1). Although many fundamental scientific principles are essential for modern Mars exploration, this paper focuses on how the study of mineralogy and rocks provide insight into the state of water and presence of organic molecules, which tell scientists about the geological history and potential of life of Mars.

To collect results from Martian minerals and rocks, scientists must use specialized equipment to analyze samples retrieved from rovers. One of these instruments is the Sample Analysis at Mars (SAM), which has three analysis functions: evolved gas analysis-quadrupole mass spectrometry (EGA), combustion, and wet chemical experiments (2). Another equipment used is the alpha-particle x-ray spectrometer (APXS). The APXS shows the chemical composition of the rocks being analyzed by x-ray fluorescence spectroscopy (3). By utilizing these instruments, scientists can determine the mineral and chemical composition of Mars’s rocks. The results from these analyses unveil mysteries of the red planet, which could help answer the question: Was there, is there, or will there ever be life on Mars?

The results from these analyses and discoveries of Martian minerals and rocks provide evidence of previously existing water on the planet’s surface. One example of these minerals is clay, which has been detected at numerous sites on Mars. The presence of clay minerals are “key indicators of an ancient habitable lake” (4). This is because clay is a common water-bearing mineral. Esperance, a clay-rich rock that was discovered by the Mars rover Opportunity, was most likely formed “from copious water running through volcanic rocks” (5). Study shows that Esperance interacted with neutral, drinking water to form (5). Evidence of water of a neutral pH is crucial in proving that life could have existed on the now barren planet. In a separate study conducted by the Mars rover Curiosity, an “unexpected abundance and diversity of clay minerals” were present in the sedimentary rocks of Gale Crater, which again indicates a former presence of surface water and a climate that was once wet (4). By looking more deeply into the cracks on the rocks, scientists also concluded that former lakes on Mars underwent “episodic drying and subaerial exposure” (4). Drying of lakes suggest that the planet had a shift in its environment that impacted the once warm and wet climate. Data from Curiosity also found dioctahedral smectite, which like clay, forms “in a variety of surface and subsurface aqueous environments” (4). In a research conducted by Bristow et al., they concluded that the formation of dioctahedral smectite led to a redistribution of nutrients which influenced gases that regulate the Martian weather (4). Both clay and dioctahedral smectite add to the theory that Mars was once a “water-rich world with conditions amenable for life,” and that there was a change in climate or atmosphere that caused the planet to become dry (5).

Besides clay and dioctahedral smectite, other minerals that provide evidence of a once watery Martian surface include opals, quartz, and hematite. The Mars Reconnaissance Orbiter discovered opal deposits, while Curiosity detected basaltic, quartz, hematite, and among other minerals in the Bagnold Dunes at the Gobabeb site (6, 3). Opals and quartz belong to a family of minerals called hydrated silicas. Hydrated silicas contain water molecules that are wedged in between silicon-based minerals, which means that it must have interacted with liquid water to form (6). Hematite, like opal and quartz, is also formed in the presence of water. The opal deposits found on Mars lie in “areas that appear to have formed only about two billion years ago,” which is younger than clay deposits that formed three point five billion years ago (6). Therefore, it was not that long ago that Mars once had a warm environment that could contain liquid water. Furthermore, dried up lake beds on Mars have accumulated many minerals, which means that liquid water “persisted for thousands of years” (6). Life requires time to evolve, so the fact that liquid water was present on the surface of Mars for a long period of time suggests that life could have developed. The discovery of minerals on Martian rocks and soil lead to many well-based hypotheses about water on Mars, which leads to a better understanding of how and when the Martian environment changed from a condition with great potential to harbor life to a lifeless desert.

Another key requirement for life, besides water, is the presence of essential organic compounds. Through past research, scientists have discovered various organic molecules in Martian rocks and soil. Mars rover Curiosity has found evidence of carbon-based compounds, which are essential for life as we know it. The rover also found evidence that there were complex organic molecules in the Gale crater about three point five billion years ago (7). These compounds are “still preserved in sulfur-spiked rocks derived from lake sediments” (7). Even though non-living processes could have created the same molecules, this finding shows that organic compounds are preserved and provides hints for scientists on where to find additional compounds. In another research conducted at Gale crater, Sheepbed mudstone was also discovered to contain “mineralogy suited for preserving organic compounds” (2). Some of these organic compounds detected were chlorobenzene, 1,2-dichloropropane, 1,2-dichloroethane, 1,2-dichlorobutane, and others (2). The fact that rocks on Mars could preserve organics prove that these compounds can persist in the extreme Martian environment. Furthermore, traces of organic compounds in the ancient sedimentary rocks give clues to how they were formed. Research analysis by Fressinet et al., concluded that rocks on Mars were either formed by natural “igneous, hydrothermal, atmospheric, biological processes” or delivered by “meteorites, comets, or interplanetary dust” (2). Organic molecules found on Mars, such as perchlorate, could also lead to an answer about water on the planet. Perchlorates lower the freezing point and evaporation rate of water, which raises the possibility that contemporary water may exist in Mars’s extreme environment (8). By studying the organic molecules present in minerals and rocks, scientists can better understand the processes and conditions under which these minerals and rocks formed.

Although scientists have already made great progress on uncovering Mars’s unknowns, minerals and rocks of Mars should continue to be studied to learn more about the planet’s environmental and geological history. By discovering and analyzing numerous samples, scientists can determine more about Mars’s past and present environmental state. Since the study of meteorite ALH84001, scientists have so far determined that Mars was once a warm and wet planet that could have harbored life. Further study would lead to a greater understanding of the potential of liquid water on the planet and give context for the potential habitability and biotic molecular signatures of Mars (2). This information will provide insight for the future of Mars exploration. Moreover, in the face of possible human exploration of Mars, this research will be crucial in determining if human exploration will be possible and if there will be life on Mars, whether by humans colonizing the planet or by natural Martian life.

References:

  1. Johnson S (2020) Sirens of Mars (Penguin Books, [S.I.]).
  2. Freissinet C, et al. (2015) Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars. Journal of Geophysical Research: Planets 120(3): 495-514.
  3. Achilles C, et al. (2017) Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars. Journal of Geophysical Research: Planets 122(11): 2344-2361
  4. Bristow T, et al. (2018) Clay mineral diversity and abundance in sedimentary rocks of Gale crater, Mars. Science Advances 4(6): eaar3330.
  5. Chang, Kenneth. “Martian Rock Another Clue to a Once Water-Rich Planet.” The New York Times, The New York Times, 7 June 2013, https://www.nytimes.com/2013/06/08/science/space/martian-rock-another-clue-to-a-once-water-rich-planet.html.
  6. Chang, Kenneth. “Minerals on Mars Point to More Recent Presence of Water.” The New York Times, The New York Times, 3 Nov 2008, https://www.nytimes.com/2008/11/04/science/space/04mars.html.
  7. Greshko, Michael. “Building Blocks of Life Found on Mars.” National Geographic, National Geographic, 7 June 2018, https://www.nationalgeographic.com/news/2018/06/mars-organic-compounds-methane-curiosity-space-science/.
  8. Kwon D “Search for Life on the Red Planet.” TheScientist, TheScientist, 1 Dec 2017, https://www.the-scientist.com/features/search-for-life-on-the-red-planet-30176