Two interesting studies published in early 2025 make light on the wet past of Mars. Scientists have detected a possible ancient beach in Mars’ northern hemisphere and identified a water-containing mineral responsible for the planet’s rosy hue.
There have always been doubts about the early period of Mars. Was it a cold, dry planet or a warm, wet planet? These two new studies, together, partially resolve the doubts: Early Mars was wet; it was never dry.
Let’s start from the iron oxide-hydroxide minerals in Martian dust that provide crucial insights into Mars’ past climate and habitability. Previous studies attributed Mars’ red color to anhydrous hematite formed through recent weathering. The new study published in February on Nature Communications, show that poorly crystalline ferrihydrite (Fe5O8H · nH2O) is the dominant iron oxide bearing phase in Martian dust, based on combined analyses of orbital, in-situ, and laboratory visible near-infrared spectra. Through laboratory experiments and kinetic calculations, They demonstrate that ferrihydrite remains stable under present-day Martian conditions. The persistence of ferrihydrite suggests it formed during a cold, wet period on early Mars under oxidative conditions, followed by a transition to the current hyper-arid environment. This finding indicates that ancient Mars experienced aqueous alteration before transitioning to its current desert state.
Mars’ northern lowlands lie at a lower elevation than the rest of the planet, leading some scientists to suspect that the area had once been the site of a vast ocean. In the second study, in fact, published on PNAS, scientists use data from the Zhurong Rover Penetrating Radar on the southern Utopia Planitia to identify subsurface dipping reflectors indicative of an ancient prograding shoreline. The rover detected a kilometer-long sloping region buried 10 to 35 meters underground that closely matches the slope of beaches on Earth. Radar data suggest that the slope is made of pebble- to sand-sized sediments. The researchers first considered the idea that the sandy slope is a buried dune, like those found elsewhere on the Martian surface. But the detected features don’t match the expected shape of windblown sand dunes, nor are they likely to be caused by rivers or lava flows. Instead, the sediment deposits resemble deposits on Earth’s coastlines. Mars may have once hosted a liquid water ocean in its northern lowlands, according to the new study.
These are hypotheses for the moment. The findings don’t demostrate that Mars hosted an ocean, but if the area does represent an ancient shoreline, it could help scientists understand more about the planet’s past potential to host life.
References
J. Li et al. Ancient ocean coastal deposits imaged on Mars. Proceedings of the National Academy of Sciences, Vol. 122, e2422213122. Published online February 24, 2025. doi: 10.1073/pnas.2422213122.
A. Valantinas et al. Detection of ferrihydrite in Martian red dust records ancient cold and wet conditions on Mars. Nature Communications. Published online February 25, 2025. doi: 10.1038/s41467-025-56970-z.
https://www.sciencenews.org/article/ancient-mars-wet-cold-planet
