Researchers at the Planetary Science Institute (PSI) in Tucson, Arizona, have found a new explanation for how seas and lakes may have once developed on Mars.
J. Alexis Palmero Rodriguez from the PSI has been studying the martian northern lowlands region, which contains extensive sedimentary deposits that resemble the abyssal plains of Earth's ocean floors. It is also like the floors of other basins on Mars where oceans are thought to have developed.
The origin of these deposits and the formation of martian lakes and seas are controversial. One theory is that there was a sudden release of large volumes of water and sediment from zones of apparent crustal collapse known as "chaotic terrains." However, these zones of collapse are rare on Mars, while the plains' deposits are widespread and common within large basin settings, Rodriguez said.
Citing evidence found in the planet's northern plains south of Gemini Scopuli in Planum Boreum, Rodriguez proposes that groundwater emerged through extensive and widespread fractures forming the floors of ancient continental-scale basins on Mars. This led to the formation of river systems, large-scale regional erosion, sedimentary deposition, and water ponding.
This model does not require sudden massive groundwater discharges, he said. Instead, it advocates for groundwater discharges being widespread, long-lived, and common in the northern plains of Mars.
"With the loss over time of water from the subsurface aquifer, areas of the northern plains ultimately collapsed, creating the rough hilly surfaces we see today," said Rodriguez. "Some plateaus may have avoided this fate and preserved sedimentary plains containing an immense record of hydrologic activity. The geologic record in the collapsed hilly regions would have been jumbled and largely lost.
"This model implies that groundwater discharges within basin settings on Mars may have been frequent and led to formation of mud pools, lakes, and oceans," Rodriguez continued. "In addition, our model indicates this could have happened at any point in the planet's history. There could have been many oceans on Mars over time."
If life existed in martian underground systems, life forms could have been brought up to the surface via the discharges of these deep-seated fluids. Organisms and their fossils may therefore be preserved within some of these sedimentary strata, Rodriguez said.