The planet Mars has captured the imagination of science fiction authors and scientists as the best candidate to finding extraterrestrial life in the solar system. The red planet has been featured in numerous movies, most recently in the Martian, as a place to establish a human research base and colony. As far as we know, the main condition for life to occur is water. Mars was likely very similar to Earth, it had a magnetic field and liquid water. Where did this vital resource go? What evidence do we have that there once was water? Let’s examine the mystery of water on Mars.
In order to understand the issue of water, we should first talk about the red planet’s atmosphere. When the planet first form, it had a much thicker atmosphere just like Earth. Nevertheless, Mars is much smaller therefore due to the lower gravity, the atmospheric gases floated off into space. This caused the planet to cool and the pressure to fall, which allowed water to sublimate and turn instantly from a solid to a gas (like CO2 dry ice). This is why we see a dry and cold red planet.
Nowadays the atmosphere has the pressure of 1% of the Earth’s atmospheric pressure at surface level. It is composed primarily of carbon dioxide, nitrogen and argon. There are some water-ice clouds that form around mountain tops, however most clouds are composed of CO2 .
But wait, you might ask, doesn’t Mars have polar ice caps? Aren’t those made of water? The sublimation of water makes it very difficult to have large liquid beds on the surface, so it accumulates in the colder regions as ice under protective sheets. These are made of dry ice or solid carbon dioxide, and change periodically just like the ice caps of the Earth. In fact, Mars experiences a lot of periodic changes in the weather, similar to the ice-ages of the Earth, suggesting that liquid water exists there in some periods. This is due to the changes in the axis of rotation tilt. Perhaps large comet impacts can also briefly create a thick enough atmosphere for liquid water.
The best evidence of past water are geological landforms. As seen with the first image, there are dried river channels on the surface of Mars. These were likely caused by permafrost in the soil being rapidly melted during a period of high volcanic activity. Another feature of little gullies and dark streaks on the sides of craters indicates very recent water flow. The gullies do not feature many crater impacts, which means they are young. The water could be coming from underground deposits, heated by the tectonic activity of the interior of Mars. In fact, a large slab of ice was found below the surface in 2015, which could have resulted from snowfall in the past.
Furthermore, other evidence lies in the large plains in the north, which could have once been an ocean. Mount Sharp was constructed using lake sediments, as the Curiosity rover has shown. Furthermore, wetter soil like clay appears near dry lakes and riverbeds. This suggests, that water was prevalent and existed for long periods of time.
If you want to explore the Martian surface for yourself try Google Mars. I recommend downloading it through Google Earth as it runs smoother. It uses satellite images and surface images from rovers to create a very immersive experience. Try looking for ice on the poles and dried riverbeds.
Many of the aforementioned discoveries happened in the 2010s, which means that with more Mars missions we will discover even more evidence and theories about water on the red planet. Perhaps the manned missions planned by Space X and NASA can accelerate progress and once and for all get down to the bottom of this mystery.
References
Evidence for Water on Mars. (n.d.). Hyperphysics. http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/mars4.html
NASA Confirms Evidence That Liquid Water Flows on Today’s Mars. (2015, September 28). NASA. https://www.nasa.gov/press-release/nasa-confirms-evidence-that-liquid-water-flows-on-today-s-mars/
Tillman, N. T. (2018, August 18). Water on Mars: Exploration & Evidence. Space.Com. https://www.space.com/17048-water-on-mars.html
Water and Life on Mars | Astronomy. (n.d.). Lumen Learning. https://courses.lumenlearning.com/astronomy/chapter/water-and-life-on-mars/
Williams, M. (2015, December 7). Mars compared to Earth. Phys.Org. https://phys.org/news/2015-12-mars-earth.html