Mars may have deep groundwater

The red planet might not be so red after all, at least on the inside. A new study from the University of Southern California Arid Climate and Water Research Center (AWARE) suggests that there could still be active deep groundwater wells on Mars, potentially resulting in surface streams in equatorial regions of the planet. The research follows a discovery by the Italian Space Agency in mid-2018 of a deep-water lake under Mars’ southern polar ice caps.

The study, published in Nature Geoscience, confirms that there is likely an active deepwater circulation system on Mars that extends far beyond just its polar ice caps. Groundwater as deep as 750 meters could be exposed to the surface through ground fractures, creating springs and surface streams in some craters that could be the basis for habitability on the red planet. Scientists previously thought that any water found on the surface was limited to just a few meters of subsurface water flow. “We suggest that this may not be true,” said Essam Heggy, a research assistant at the University of Southern California and NASA’s Jet Propulsion Laboratory, in a statement. “We propose an alternative hypothesis that they originate from a deep pressurized groundwater source which comes to the surface moving upward along ground cracks.”

The researchers propose that fractures within Mars’ craters enable springs to rise to the surface due to tremendous pressure within the planet, as evidenced by seasonal dark streaks called recurring slope lineae that appear on Mars during warm parts of the year. “The system shuts down during winter seasons, when the ascending near-surface water freezes within fault pathways, and resumes during summer seasons when brine temperatures rise above the freezing point,” the paper explains.

In order to explore how Mars’ groundwater arrives on the planet’s surface, the researchers used high-resolution optical imagery and computer modeling to investigate the walls of large impact craters, attempting to correlate the presence of fractures with the sources of dark streaks and flowing surface water streams. This is different from previous work, which has focused on interpreting electromagnetic echoes returned from radar-probing instruments aboard the Mars Express and Mars Reconnaissance Orbiter. However, the existing methodology was not sufficient to determine that there is groundwater in a broad geographical range outside of Mars' south pole.

According to Heggy and University of Southern California postdoctoral researcher Abotalib Z. Abotalib, their experience studying a similar phenomenon in the Sahara Desert on Earth helped them achieve their goals. “The experience we gained from our research in desert hydrology was the cornerstone in reaching this conclusion. We have seen the same mechanisms in the North African Sahara and in the Arabian Peninsula, and it helped us explore the same mechanism on Mars,” said Abotalib. Heggy added, “Groundwater is strong evidence for the past similarity between Mars and Earth — it suggests they have a similar evolution, to some extent.”

Heggy is excited about the intrigue his study has created within the scientific community. While some disagree on this paper’s explanation for recurring slope lineae on Mars, the debate furthers extraterrestrial water science and water science education in arid areas and could fuel development of more advanced probing systems.

“Understanding how groundwater has formed on Mars, where it is today, and how it is moving helps us constrain ambiguities on the evolution of climatic conditions on Mars for the last three billion years and how these conditions formed this groundwater system. It helps us to understand the similarities to our own planet and if we are going through the same climate evolution and the same path that Mars is going,” Heggy explained. “Understanding Mars' evolution is crucial for understanding our own Earth's long-term evolution and groundwater is a key element in this process.”