In 1973, David Bowie posed the question: “Is there life on Mars?”
Now, 42 years later, scientists are finally getting back to him. Well, they sort of are. Actually, not at all, since we still don’t know whether there is life on Mars. However, on Sept. 28, scientists confirmed that there is liquid water on the Martian surface. Scientists already knew that there was water on Mars in the form of polar ice caps and glaciers. They also suspected that Mars once had rivers, lakes and perhaps even oceans. However, it was not until a few days ago that they had definitive proof.
From the Mars Reconnaissance Orbiter, a team of scientists observed streaks that flow down the slopes of craters, canyons and mountains during the summer months and then fade away during the winter months. These streaks, which the team named Recurring Slope Lineae (RSL), appear during the summer months when water saturates the streaks and causes them to appear darker. As the planet cools, the water freezes and the streaks fade.
Scientists believe that the streaks are not evidence of liquid water itself, but that the absorptions are evidence of hydrated salts. Salts such as magnesium perchlorate, magnesium chlorate and sodium perchlorate absorb water like sponges. The salts lower the freezing point of water to 80 Kelvin, allowing the water to stabilize into its liquid state. RSL are the result of those salts becoming waterlogged, darkening the surface of the planet.
But where is this water coming from? Scientists actually don’t know yet, although they do have some theories. Some say that water could come from melting ice located at or below the surface. However, it is unlikely that there is ice so close to the equatorial surface. Others say that the water is coming from the atmosphere, but Mars’ atmosphere contains very little humidity. A third theory suggests that an underground layer of water, called an aquifer, lets out a discharge of water seasonally, causing the RSL. Still, it is unclear how the water from the aquifer would be able reach higher altitudes to account for the RSL that appear on mountain peaks.
Although the discovery of the RSL warrants further exploration, NASA has barred robotic explorers from those areas because it fears the robots might contaminate Mars by carrying microbes into the Martian landscape. A spacecraft can be sterilized, but the process is very difficult and expensive since it requires electronics and technologies that can withstand the necessary temperatures. NASA plans to send another craft out in 2020 to investigate the regions, but it is unlikely that it will be sterile enough to directly explore the RSL.
Let’s return to Bowie’s long-unanswered question, “Is there life on Mars?” We know now that there’s water on Mars, but is it enough to support life? Many scientists are skeptical. The liquid water on Mars is incredibly salty—so salty that some scientists believe it cannot sustain life. Other scientists are more hopeful. Four RSL have been found thus far, and it is possible that the conditions of each are different; perhaps one of the streaks is not as salty as the others and can support life. Despite the numerous challenges that NASA now faces, it is still a step closer to discovering whether life can exist and be maintained on Martian soil.
So until then, David Bowie, keep singing.