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Mars was once a planet teeming with surface water. However, the extent to which water is still present in the planet’s crust remains a subject of scientific inquiry, according to a recent analysis.
Over 3 billion years in the past, there were periods during which liquid water covered Mars’ surface. Following the loss of much of its atmosphere, the environment became inhospitable for sustaining surface water. The ultimate fate of this water—whether it has become trapped as ice, stored in deep aquifers, integrated into minerals, or lost to space—continues to be actively researched. This subject holds particular significance for Bruce Jakosky, a senior research scientist at LASP and the former principal investigator of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission.
In a recent letter to the editor featured in the Proceedings of the National Academy of Sciences (PNAS), Jakosky disputes conclusions drawn from a 2024 study published in the same journal, which asserts that substantial liquid water persists in Mars’ mid-crust. He argues that while this suggests one interpretation of the findings, it is not the only possible scenario, as the underlying data do not necessarily indicate a water-saturated crust.
“While the methodology and analysis presented are sound, the modeling results allow for alternative interpretations,” Jakosky asserts.
The research referenced was derived from NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission, which was initiated in 2018. This mission deployed a lander on Mars to gather geophysical information aimed at exploring the planet’s interior. Although the mission concluded in 2022 due to a Martian dust storm that impaired the lander’s solar panels, scientists continue to scrutinize and debate the data collected by InSight.
In a study published in August 2024, geophysicist Vashan Wright, affiliated with the Scripps Institution of Oceanography at the University of California, San Diego, along with his team, utilized rock physics models to analyze the types of rocks, levels of water saturation, and pore space characteristics that could explain the seismic and gravity data gathered from the mid-crust, which lies approximately 11.5 to 20 kilometers below the Martian surface.
The researchers posited that a mid-crust consisting of fractured igneous rocks saturated with liquid water would most accurately account for the existing data. Their estimates suggested that the volume of entrapped water might equate to a thickness of one to two kilometers if disseminated evenly across the Martian surface, a concept referred to as the global equivalent layer. For context, Earth’s own global equivalent layer, which is primarily attributable to its oceans, measures 3.6 kilometers—with minimal water present in the crust.
“We anticipate the existence of either water or ice in the crust,” Jakosky stated, highlighting the difficulty yet importance of detecting and quantifying it to fully understand Mars’ hydrological history.
In evaluating the findings, Jakosky considered various factors, such as pore space distribution and the likelihood of existing solid ice or voids. He emphasized that while InSight’s data does not necessitate the presence of water in the mid-crust, it does not exclude it either. After considering these various attributes, he revised earlier estimates to propose that the global equivalent layer could range from zero to two kilometers, thus broadening the lower limits established by previous research.
The investigation into the quantity of water within Mars’ crust remains open, with future missions planned to provide more comprehensive geological assessments and enhanced seismic profiling. The implications of such findings could significantly contribute to our understanding of the Martian water cycle, the planet’s potential to support life, and the availability of resources essential for future explorations.
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