NASA’s Mars Science Lab (MSL) Mission of 2011 is no stranger to us. The landing of the Mars rover ‘Curiosity’ in the Gale Crater in August 2012 proved to be a great asset in investigating Mars' habitability, its climate and geology, and in collecting data for a human mission to the Red Planet. [1]
Self-portrait of Curiosity at the foot of Mount Sharp in Mars, October 2015; Image source: Wikipedia
In December 2012, we saw the extensive soil analysis by Curiosity which revealed the presence of water molecules, sulfur, and chlorine in Martian soil. [2,3] In March 2013, the existence of mineral hydration was discovered. [4,5] Finally, the rover’s DAN (Dynamic Albedo of Neutrons) instrument provided evidence of subsurface water, with as much as 4% water content at a depth of 60 cm. [4] Chemically-bound water was found in soil samples at the Rocknest region of Aeolis Palus in Gale Crater in September 2013. [6] On December 9, 2013, NASA reported that the Gale Crater once had a freshwater lake. [7] In October 2015, we saw NASA’s Curiosity team confirm the presence of lakes and streams in the Gale Crater about 3.3–3.8 billion years ago. Based on the Gale Crater studies, geologists finally provided solid evidence regarding the existence of abundant water resources on early Mars, about 3.3 to 3.8 billion years ago. [8] By November 2018, the media made this discovery popular amongst the laymen. [9]
Aeolius Mons rises from the middle of the Gale Crater; Image source: Wikipedia
The knowledge of the existence of water on early Mars by the use of such probes is bound to create questions in your minds: Does water exist on Mars at present, in real-time?
To answer this question, let’s take you back to the time of Mariner 9.
Mariner 9 satellite; Image source: Wikipedia
Mariner 9 was launched in May 1971, almost 5 decades back, and became the first satellite to orbit another planet. [10] This orbiter discovered the existence of ice in Martian northern (Planum Boreum) and southern (Planum Australe) polar caps. [11] Martian ice in the polar caps is no surprise since the planet is known to have a bitterly cold climate in its polar regions, because of its thin atmosphere and the planet being located away from Sun. [16] Temperatures there drop low enough to freeze both water and carbon dioxide, making Mars a planet with two kinds of ice. The observations from NASA’s Viking Project in the 1970s showed the seasonal carbon dioxide cover at the northern polar cap to be only about a meter thick, which disappears each summer, leaving behind a perennial water ice cap.
North Polar Ice Cap; Image source: Wikipedia
In the southern polar cap, the scientists thought that the seasonal CO2 deposit lay on top of a thicker CO2 cover, covering a water ice cap. It was in February 2002 that a much more precise image of the southern polar ice cap by the satellite Mars Odyssey was obtained. This, as expected, showed a polar covering of CO2 ice, i.e. dry ice. Away from the polar cap, a warm ground of dry soil was detected. Between them, a patch of plain water ice covered with a thin layer of dust was also identified. [12]
South Polar Ice Cap; Image source: Wikipedia
Now that we have an answer to the previously asked question, we come to the most recent discovery about the water on Mars. Would you believe it if you came across something like the Martian Grand Canyon? Probably not.
The Grand Canyon National Park of northwestern Arizona, USA, is known to house one of the Wonders of the World, The Grand Canyon, which is a gorge of the Colorado River. The park covers 4,926.08 sq. km of unincorporated area in the Coconino and Mohave counties. [17] While Arizona's Grand Canyon is no new news, the Martian Grand Canyon comes off as quite a peculiar case as it is quite an unknown concept. The Martian Grand Canyon, Valles Marineris, is suggested to be a large tectonic crack on Mars’ crust [13] and is located along the equator of Mars; it is considered to be the largest canyon in the Solar System.
Valles Marineris as seen in Viking 1 orbiter image mosaic; Image source: Wikipedia
Let’s take a look at the most recent discovery of water on Mars. The European Space Agency’s Mars Express has sought to hunt for near-surface water, ranging from the water locked up in minerals to that in the ice covering the dust grains in soil. Sadly, only small amounts of water were found, that too on the very surface in the lower latitudes of the planet. Water ice is not found on the surface near the equator, rather it is hidden beneath the Martian surface because naturally, the temperatures here are not cold enough for the exposed ice to stay intact.
In December 2021, deeper water stores well-hidden beneath the Martian surface were rediscovered more accurately and precisely. You must be wondering why Valles Marineris was introduced earlier and how it relates to these water stores. This is because a significant amount of water has been found at the heart of the Martian Grand Canyon, which lies near the equator. It was ESA’s Roscosmos ExoMars Trace Gas Orbiter that became the hero of this recent discovery. Trace Gas Orbiter’s (TGO) Fine Resolution Epithermal Neutron Detector (FREND) participated in mapping the hydrogen – a measure of water content – in the uppermost meter of Mars’ soil.
TGO; Image source: ESA
Dr. Igor Mitrofanov of Russia's Institute for Space Research (IKI) in Moscow, the principal investigator of the high-energy neutron detector on the 2001 Mars Odyssey mission and the lead author of this new study said, “With TGO, we can look down to one meter below this dusty layer and see what’s really going on below Mars’ surface – and, crucially, locate water-rich ‘oases’ that couldn’t be detected with previous instruments. FREND revealed an area with an unusually large amount of hydrogen in the colossal Valles Marineris canyon system… assuming the hydrogen we see is bound into water molecules, as much as 40% of the near-surface material in this region appears to be water.” [14]
Valles Marineris; Image source: ESA
The so-obtained FREND observations from May 2018 to February 2021 was analyzed by Igor and colleagues, which aimed at mapping the hydrogen content of Martian soil by detecting neutrons rather than light. [15]
Quoting Dr. Alexey Malakhov of the Space Research Institute, “Neutrons are produced when highly energetic particles known as ‘galactic cosmic rays’ strike Mars… drier soils emit more neutrons than wetter ones, and so we can deduce how much water is in a soil by looking at the neutrons it emits.”
ExoMars TGO maps the water-rich region of Valles Marineris. As reflected on these scales, the purple contours at the centre of this figure show the most water-rich region. In the area marked with a ‘C,’ up to 40% of the near-surface material appears to be composed of water (by weight). The area marked ‘C’ overlaps with the deep valleys of Candor Chaos and is promising in the hunt for water on Mars. The underlying grey shading in this image represents surface topography and is based on data from the MGS/MOLA Mars Global Surveyor Mars Orbiter Laser Altimeter [18]. The axes around the frame show location on Mars; Image source: Mitrofanov et al., 2021. [15]
He continues, “We found a central part of Valles Marineris to be packed full of water – far more water than we expected. This is very much like Earth’s permafrost regions, where water ice permanently persists under dry soil because of the constant low temperatures.” This newly found water could be ice or chemically bound to minerals in the soil. But previous observations prove that the minerals here typically contain less water than as specified by these newer observations. Thus, this water is most likely to be ice, as is Dr. Alexey’s opinion. [14]
Keeping in mind the fact that the temperature and pressure conditions near the Martian equator will cause this water ice to disappear, there must be some sort of replenishment or preservation of water in Valles Marineris, which is still unclear to researchers.
Nevertheless, this finding is a promising first step, and there is a great deal of observation required to know the form of water being dealt with. Regardless of the form of water, since the exploration of Mars has been a global subject of interest, the discovery of water on Valles Marineris will turn out to be a target for future exploration missions.
References
[1] Beutel, Allard (November 19, 2011). "NASA's Mars Science Laboratory Launch Rescheduled for November 26". NASA. Retrieved November 21, 2011.
[2] Brown, Dwayne; Webster, Guy; Neal-Jones, Nance (December 3, 2012). "NASA Mars Rover Fully Analyzes First Martian Soil Samples". NASA. Archived from the original on December 5, 2012.
[3] Chang, Ken (December 3, 2012). "Mars Rover Discovery Revealed". New York Times.
[4] Webster, Guy; Brown, Dwayne (March 18, 2013). "Curiosity Mars Rover Sees Trend In Water Presence". NASA. Archived from the original on March 22, 2013.
[5] Rincon, Paul (March 19, 2013). "Curiosity breaks rock to reveal dazzling white interior". BBC.
[6] Lieberman, Josh (September 26, 2013). "Mars Water Found: Curiosity Rover Uncovers 'Abundant, Easily Accessible' Water In Martian Soil". iSciencetimes.
[7] Chang, Kenneth (December 9, 2013). "On Mars, an Ancient Lake and Perhaps Life". New York Times.
[8] Clavin, Whitney (October 8, 2015). "NASA's Curiosity Rover Team Confirms Ancient Lakes on Mars". NASA. Retrieved October 9, 2015.
[9] Geological Society of America (November 3, 2018). "Evidence of outburst flooding indicates plentiful water on early Mars". EurekAlert!. Retrieved November 5, 2018
[10] "Mariner 9: Details". National Space Science Data Center. Retrieved December 28, 2011
[11] Cutts, James A. (July 10, 1973). "Nature and origin of layered deposits of the Martian polar regions". Journal of Geophysical Research. 78 (20): 4231–4249. doi:10.1029/JB078i020p04231.
[12] Mars Odyssey Themis, Water ice confirmed at Mars' south polar cap [Online]. Available at: https://themis.mars.asu.edu/node/5392 (Accessed: 08 February 2022)
[13] Wolpert, Stuart (2012-08-09). "UCLA scientist discovers plate tectonics on Mars". UCLA. Retrieved 2012-08-13.
[14] Sci News (December 17, 2021), ESA’s Trace Gas Orbiter Finds Water in Martian Canyon System [Online]. http://www.sci-news.com/space/valles-marineris-water-10378.html (Accessed: 08 February 2022)
[15] Mitrofanov, I., Malakhov, A., Djachkova, M., Golovin, D., Litvak, M., Mokrousov, M., Sanin, A., Svedhem, H. and Zelenyi, L., 2022. The evidence for unusually high hydrogen abundances in the central part of Valles Marineris on Mars. Icarus, 374, p.114805.
[16] Sharp T., Gordon J. (2022), What is the temperature on mars [Online]. Available at: https://www.space.com/16907-what-is-the-temperature-of-mars.html (Accessed: 08 February 2022)
[17] Wikipedia, Grand canyon national park [Online]. Available at: https://en.wikipedia.org/wiki/Grand_Canyon_National_Park (Accessed: 08 February 2022)
[18] Goddard Space Flight Center, The mars orbiter laser altimeter [Online]. Available at: https://attic.gsfc.nasa.gov/mola/ (Accessed: 08 February 2022)
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