Planet Mars and Potential for Life

Mars is a medium-sized world about the half diameter of Earth and its surface is old, cratered, and marked by volcanoes. Compared to Earth, Mars has also a differentiated internal structure composed of the outer crust, mantle, and core. It appears red because of the rust in its thin atmosphere and it is the home to some of the largest planetary features including Olympus Mons, and Valles Marineris.

Figure 1 : (a) - Earth or Mars? The NASA rover Opportunity found blueberry-size spheres of Hematite on the Martian surface, which (1) point out are strikingly like these larger Hematite ‘marbles’ found in Utah (b).

In 2003, NASA launched two rovers to Mars. One of these rovers called Opportunity was landed in a 22m diameter crater in a region named Terra Meridiani (1). This rover has indicated Hematite in form of spheres embedded in rock outcrops near the crater rim (Figure 1-a). These blueberry-size spheres of Hematite on the Martian surface are extremely similar to the larger Hematite ‘marbles’ found in Utah (Figure 1-b) (2).

The missions of the past few decades show that Mars is cold, arid, rocky and its atmosphere contains approximately 96 percent of carbon dioxide (3). All discoveries have revealed that Martian wasteland was previously a volatile world, where volcanoes once raged, meteors plowed deep craters, and flash floods rushed quickly over the land-atmosphere (3). Therefore, the Red Planet still throws out new enticements with each landing or orbital pass made by a spacecraft.

Physiography

Physically, Mars’s surface could be divided into two territories (Figure 2). The first territory appears in the northern hemisphere defined mainly by smooth plains layered by a thin covering of deposits consisting of lava flows and sediments (4). These northern plains are approximately five kilometers lower than the second territory which occurred for the most part in the southern hemisphere and is marked with densely cratered highlands (4). These impact craters that characterize the southern highlands were accumulated due to a regular fall of comets and asteroids which proves that the southern highlands are older than the northern smooth plains (4). Several studies show that despite the uncertainty regarding the absolute age of these highlands, in all probability they are the age of around 4 billion years (4).

Figure 2: Color-coded elevation map highlighting key physical features of Mars. Red is high elevation, blue is low elevation. Adapted from map of Mars' elevation from NASA/JPL.

Unlike on Earth, Mars has no tectonic plates, which means the tectonic activity on this planet is most likely extinct (similarly to the Moon). However, Mars is characterized by a region called Tharsis (4), it contains the five biggest volcanoes in the solar system, and they rise to an elevation of 27 kilometers. This region is surrounded by tectonic features constituted by certain movements of the lithosphere (4). Compared to Earth, Mars also has polar ice caps, both are identified by layers consisting of clean and dust water ice changing alternately at the top of a stacked layer of sediments, and a transitory frost covers both ice caps during winter. The most dominant part of this ephemeral frost is mostly determined by carbon dioxide (4).

Atmosphere, Weather, and Frozen Volatiles

Mars’s thin atmosphere consists mostly of 95% carbon dioxide and the rest includes nitrogen and argon with small portions of trace gases (oxygen and carbon monoxide). It affects heavily Mars’surface which makes water quickly evaporate once it starts melting from ice due to low pressure, except salty water that might stay longer due to its salt content in the warmest places (3). In contrast, weather on Mars is dynamic, it is commonly characterized by water ice clouds. The image below (Figure 3-a) was taken by Mars Orbiter Camera (MOC) from Mars Global Surveyor (MGS) shows how repeatable these clouds are, they are formed in the same spot every year in the period from 1997 to 2006 (5). The southern hemisphere is mostly known as a cloud of dust, they exist mostly in spring and summer, and that brings back the famous dust events (Figure 3-b) which occurred the same year as Mariner 9 arrived at Mars (5).

Figure 3 : (a) - Water ice occurs on Mars' surface in the residual polar caps. (b) - Light-colored, tongue-shaped dust storm extending down and to the left of the northern seasonal polar cap (Image credit NASA/JPL/Malin Space Science Systems). (c) – A scarp in Chasma Boreale (Image credit NASA/JPL/University of Arizona/Planetary Science Institute).

Polar ice caps disappeared seasonally and they left a stratified sedimentary deposit positioned under the remaining cap known as “residual cap” (6). The image above (Figure 3-c) shows a scarp in Chasma Boreale which consists of the residual cap of the north polar and the sedimentary deposits stratified into polar layered deposits (red arrow), a basal layer made of sand (blue arrow), a part of this layer eroded to constitute a massive field of dunes around polar layer deposits (white arrow).

Up until this point, scientists are still wondering whether Mars’s atmosphere was always thicker or the temperature might affect its composition. This question makes some scientists think that the greenhouse effect could be the reason by which the planet is warmer today. Conversely, other scientists suggest that geothermal heating is what could justify this scenario.

Flowing Water Features

According to the NASA CRISM website, there are three different kinds of channels which possibly formed by flowing water and they vary in age and characteristics. Valley networks (Figure 4-a) are the oldest ones, they mostly occur in the southern highlands and they are the age around 3.8 billion years, they are really old that several studies explained that this class of channels is a part of ancient Martian rivers. The second category is named outflow channels (Figure 4-b), they are widely located in the eastern Valles Marineris and they arise importantly at the fault zone. Then, the youngest class of these channels known as Gullies (Figure 4-c), differ in location but most of them occur at mid-latitudes.

Figure 4 : (a) – Valley networks. (b) – Broad outflow channels cut by the catastrophic release of liquid water (Images credit NASA/JPL-Caltech). (c) – Gullies (Image credit NASA/JPL/Malin Space Science Systems). (d) - Enhanced-color image shows a dark, reddish slope "recurring slope lineae" (Image credit NASA/JPL/the University of Arizona).

Additionally, Mars’surface is marked by some sinuous features, the most common class of these features known as RSL (Recurrent Slope Lineae). The image above (Figure 4-d) shows the Hale crater marked by plenty of narrow streaks defined by “Recurring Slope Lineae” (7). These features are supposed to be made of the seasonal flow of water. On September 28th, 2015, scientists found proof of hydrated salt on this crater by using CRISM observation, meaning that Hale streaks could likely be formed by briny water (7).

Somehow, Mars tends to be slightly different from Earth in many ways when it comes to variables such as temperature, size, and atmosphere. The geologic processes on both are surprisingly similar, there are volcanoes, water erosion, dunes, and impact basins much like as found on Earth, many of the same physical land features known on our homeworld also exist on this planet to shape the Martian environment. These two planets share several similarities. However, they are very different planets.

Nowadays, what is still ambiguous is whether Mars has ever developed organic chemistry or not. If so, can Mars be a habitable world? Well, this question summarize the main purpose of the Mars Exploration Programs of different space agencies around the world. These science-driven programs are searching for proof to find out how geologic, climatic, and other processes interact to change the environment of the Red Planet over time.

References

(1) Livio, M. (2005). Cosmology and life. In M. Livio, I. N. Reid, & W. B. Sparks (Eds.), Astrophysics of Life (1st ed., pp. 98–110). Cambridge University Press. https://doi.org/10.1017/CBO9780511536113.011

(2) Chan, M. A., Beitler, B., Parry, W. T., Orm?, J., & Komatsu, G. (2004). A possible terrestrial analog for haematite concretions on Mars. Nature, 429(6993), 731–734. https://doi.org/10.1038/nature02600

(3) Seeds, M. A., & Backman, D. (2010). Astronomy: The Solar System and Beyond. 507

(4) CRISM Website. JHU/APL. Retrieved February 1, 2021, from https://crism.jhuapl.edu/science/geology/physiography.php

(5) CRISM Website. JHU/APL. Retrieved February 1, 2021, from https://crism.jhuapl.edu/science/geology/frozen.php

(6) Phillips, R. J., Davis, B. J., Tanaka, K. L., Byrne, S., Mellon, M. T., Putzig, N. E., Haberle, R. M., Kahre, M. A., Campbell, B. A., Carter, L. M., Smith, I. B., Holt, J. W., Smrekar, S. E., Nunes, D. C., Plaut, J. J., Egan, A. F., Titus, T. N., & Seu, R. (2011). Massive CO2 Ice Deposits Sequestered in the South Polar Layered Deposits of Mars. Science, 332(6031), 838–841. https://doi.org/10.1126/science.1203091

(7) Recurring “Lineae” on Slopes at Hale Crater, Mars – NASA’s Mars Exploration Program. Retrieved February 2, 2021, from https://mars.nasa.gov/resources/7487/recurring-lineae-on-slopes-at-hale-crater-mars/