NASA has produced strong evidence supporting the presence of flowing liquid water on Mars.

The case for flowing liquid water on the Red Planet has been growing since 2011, when Dr. Alfred S. McEwen, a professor of planetary geology at the University of Arizona, observed dark streaks descending slopes of craters, canyons, and mountains on the Martian surface. Officially known as recurring slope lineae (RSLs), the streaks would appear to darken during the spring and summer seasons and then dissipate during the colder months that followed. The streaks were theorized to be a product of liquid flowing water, but this remained unconfirmed until the discovery of hydrated perchlorate salts within the RSLs. According to Dr. McEwen and others, hydrated salts can only be produced in the presence of liquid water and would only be observable for a few days following the water’s evaporation.

The presence of water on Mars was not debated prior to this announcement, but the only known water was thought to be in the polar ice caps. Indeed, the average temperature on Mars is minus 70 degrees Fahrenheit (minus 57 degrees Celsius), well below the normal freezing point of water. The RSLs, however, are able to flow as a liquid because the perchlorate salt content lowers the freezing point of the water considerably, keeping it liquid at a minimum of minus 10 degrees Fahrenheit (minus 23 degrees Celsius). Scientists are unaware of the source of the water, but theorize that it might come from underground aquifers or condense out of the atmosphere in a process known as deliquescence.

NASA collected data on the RSLs using the Mars Reconnaissance Orbiter, a satellite in operation since 2006. Specifically, the agency utilized an on-board imaging spectrometer that detected signatures of the hydrated salts where the dark streaks had been seen by the orbiter’s camera. However, the camera that first observed the RSLs were capable of zooming in much closer than the spectrometer. The RSLs have been observed in multiple locations, although each one is only a few meters wide by a couple hundred meters long. The spectrometer was never meant to examine such small features from orbit. Due to this technical limitation, “New techniques and novel ways” were required to analyze the chemical signature of the dark streaks, according to Lujendra Ojha, a graduate student at the Georgia Institute of Technology.

The announcement of liquid water on Mars is particularly important given that liquid water is considered to be an essential requisite for life. Therefore, this discovery dramatically increases the probability of finding microbial Martian life either on the surface or within the crust. However, scientists caution that the detected salts may have been a barrier themselves to the development of life within the RSLs. These scientists point to Don Juan Pond in Antarctica, which remains liquid year-round due to high calcium chloride content, yet is completely devoid of life.

Unfortunately, for the foreseeable future, the RSLs will remain unexplored by the Curiosity and Opportunity Martian rovers. While unlikely, there are concerns that microbes from Earth may have survived the trip to Mars and could potentially contaminate Martian habitats. While sterilizing rovers is possible, the process increases the cost of the equipment and the complications of the design. The next Martian rover, due to be launched in 2020, will also be unsterilized.

Beyond increasing the probability of finding extraterrestrial life, the confirmation of liquid water on Mars is likely to impact the eventual human exploration of the planet. For example, hydrogen and oxygen can be separated from water to make rocket fuel, greenhouses can be more easily maintained and reverse osmosis can filter even the saltiest water into drinking water. Whether the water is a habitat for Martian microbes or a resource to be exploited by future astronauts, the discovery of liquid water on Mars is an important step for science, humankind, and the search for life elsewhere in the universe.



Chang, K. (2015, September 28). Mars Shows Signs of Having Flowing Water, Possible Niches for Life, NASA Says. Retrieved September 29, 2015.

Cookson, C. (Ed.). (2015, September 28). Nasa scientists discover ‘flowing’ water on surface of Mars – Retrieved September 29, 2015.

Anderson, G. (Ed.). (2015, September 28). NASA Confirms Evidence That Liquid Water Flows on Today’s Mars. Retrieved September 29, 2015.

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