Is there water on Mars?

Earth is the only planet in our solar system that has liquid water on its surface. However, this was not always the case. Over a billion years ago, Mars hosted vast amounts of liquid water that came in the form of rivers, lakes, seas, and maybe even oceans. Today, Mars is a dry, barren world, with the only surface water in the form of ice at its poles. Interestingly, there is evidence that liquid water may still exist deep underground on Mars. What happened to the water of Mars and what evidence is there that it once existed and may still exist?

evidence of past water

The first concrete evidence that Mars once had flowing water came from NASA’s Curiosity and Opportunity rovers. Most of the evidence for liquid water comes from chemical analysis of rocks, which often contain compounds that can only form in the presence of liquid water. The surface of Mars is dominated by a type of rock called basalt. Although basalt generally forms through volcanic activity, the chemical composition of basalt can be altered in the presence of liquid water. Basalt can absorb water into its structure, causing the rock to weather with other rocks that contain evidence of water. By analyzing the composition of Martian rocks, scientists can look for chemicals known to form only in the presence of liquid water. To date, many of the chemicals on Earth that form in liquid water have been found in Martian rock, a strong indication that liquid water was once abundant.

Although the first concrete evidence of ancient water on Mars came from rovers in the 2010s, the first evidence of liquid water actually came from Mars orbiters in the 1970s. In 1971, NASA’s Mariner 9 spacecraft captured some of the highest-resolution images of Mars at the time. The spacecraft found geological structures that looked similar to structures on Earth formed from liquid water. These included river channels, stream channels, deltas, and large sedimentary deposits. Mars itself is covered with thousands of geological structures that likely formed in the presence of liquid water. In addition, the existence of so many structures suggests that Mars held vast amounts of liquid water for a very long time. In fact, some evidence suggests that Mars managed to hold some amount of liquid water on its surface until 600 million years ago, a relatively short period compared to Mars’ 4.5 billion year history.

What happened to the water of Mars?

Unfortunately, Mars no longer has a strong magnetic field capable of deflecting solar radiation. Without a magnetic field, the solar wind has slowly stripped Mars of its atmosphere. Without a dense atmosphere, water could no longer exist in liquid form at the surface. The disappearance of the magnetic field led to the disappearance of the atmosphere, which in turn caused Mars to lose all of its surface water.

Evidence of current water

Mars has very likely had large amounts of liquid water in the past, but it may still have some liquid water. Surface temperatures and atmospheric pressure make it impossible for liquid water to form and exist on the surface of Mars, and if liquid water still exists on Mars it would have to exist underground. In 2011, an observational study of Mars found some evidence suggesting the presence of salt water underground. Scientists have known for some time about the existence of strange, dark slopes on Mars called returning slope lines (RSL). RSL are large streaks that appear on some slopes of Mars during the warmer seasons. In 2011, NASA announced that one explanation for these dark slopes was that small amounts of liquid water had melted and flowed downhill, causing the presence of these dark lines. During the summer months temperatures are still quite cold, dropping to minus nine degrees Fahrenheit (minus 23 degrees Celsius). Although this is still below the freezing point of water, water that contains enough salt actually has a lower freezing point. So even at these colder temperatures, salt water could become liquid. Additionally, as the water evaporated, it would leave behind a chemical signature that could be observed. In 2015, spectral analysis of RSL revealed a chemical composition consistent with predictions for liquid water. Although this seems to prove that liquid water still exists on Mars, later studies have suggested other explanations, and further spectral analysis has contradicted previous studies. It is not yet known whether there is still liquid water on Mars.