A recent study published on Thursday unveiled polygonal underground structures formed millions of years ago on Mars, suggesting unusual water-related activity in the Utopia Planitia region. The Chinese rover "Zhurong," which landed on Mars in May 2021, has been instrumental in this discovery. The rover has been analyzing sediments in Vastitas Borealis, a low plain in the northern hemisphere of Mars, where it collected vital data to understand the planet's climatic history.
An international team of scientists has discovered definitive evidence of an ancient ocean in the Utopia Planitia region, which has long been hypothesized to have been part of an ancient ocean that covered the northern lowlands of Mars. The evidence found by the Zhurong rover includes traces of beaches that may have been adjacent to water, as well as geological features indicative of an ancient coastline. These features include "hollow cones, polygonal grooves, and traces of flows," according to Bo Wu, a planetary scientist at Hong Kong Polytechnic University and lead author of the study published in the journal Scientific Reports.
"We estimate the flooding of the Utopia Planitia on Mars was approximately 3.68 billion years ago. The ocean surface was likely frozen in a geologically short period," Bo Wu said. The researchers concluded a scenario in which the ocean formed due to floods about 3.7 billion years ago, then froze, creating a coastline, and then dried up about 3.4 billion years ago. Over the following 230 million years, the ocean on Mars retreated until it disappeared completely.
The Zhurong rover worked on the surface of Mars for just under a year before becoming inactive due to a sandstorm and the Martian winter. Despite its limited operational period, it provided significant insights into the Martian surface and subsurface structures. The rover's findings, combined with data from China's Tianwen-1 Orbiter and NASA's Mars Reconnaissance Orbiter, indicate the existence of a water ocean during a period when Mars might already have become cold and dry and lost much of its atmosphere.
The discovered evidence includes coastal landforms along the possible shoreline and the depositional behavior of the Vastitas Borealis Formation (VBF) unit, supporting a sedimentation mechanism involving heavily silted water. This is consistent with distinctive geological features such as troughs, sediment channels, and mud volcano formations indicative of an ancient coastal area. The VBF deposits are mainly composed of fine-grained materials, suggesting a sedimentary nature likely formed from fluvial, lacustrine, or marine sediments.
Remote sensing observations were supplemented with in situ analysis to unveil features consistent with the existence of a nearshore zone in southern Utopia Planitia, indicating a significant amount of water in this region. Widely spread water and ice-related landforms in southern Utopia enhance the understanding of Mars's evolution, particularly regarding the potential for ancient water bodies.
However, not all scientists are convinced of the conclusions drawn from the data. Benjamin Cardenas, a scientist who analyzed other indicators of the possibility of an ocean, has questioned the accuracy of the recent discoveries. He believes the researchers may not have adequately considered the impact of Martian winds on sediment movement. Cardenas stated to the French news agency AFP: "There is a tendency to consider Mars not very active, like the Moon, but it is active!"
Bo Wu acknowledged that winds may have caused some rocks to erode but clarified that his research team "does not claim that the results conclusively prove the existence of an ocean on Mars." He added that meteorite impacts can "bring rocks and sediments from beneath the ground to the surface from time to time." This level of proof is likely to require sending a spacecraft to collect Martian soil samples and return them to Earth for examination.
Despite the ongoing debate, Cardenas confirmed that he leans "toward believing in the existence of an ocean on Mars." He reminded that "most scientists believe that life forms on Earth originated either at the bottom of the oceans where there were hot gases and minerals beneath, or near the surface in small tidal pools." He added, "The possible evidence of an ocean makes the planet seem more hospitable, and thus, evidence of the existence of an ocean makes the planet seem more suitable for the existence of biological forms of life."
The study further suggests an evolution scenario for the nearshore zone in southern Utopia in the context of the Martian ocean theory, enhancing the likelihood that the southern Utopia Planitia region may have hosted a large body of water. These missions are building a coherent picture of what Mars was like, but there are still missing pieces of the puzzle. Determining the truth in this area could help solve a larger mystery: whether Earth is the only planet that can host forms of life in the solar system.
A mission further north from the Zhurong landing site might find more irrefutable evidence that there was an ocean on Mars and what that ocean might have been like. The combination of these factors allows the assumption of the presence of an extensive reservoir of water and mud in southern Utopia Planitia. The analysis enhances the understanding of Mars's evolution, particularly regarding the potential for ancient water bodies in southern Utopia.
Sources: IFLScience, Nature, Live Hindustan, Asharq Al-Awsat (English), Newsweek, The Independent, Futura Science
This article was written in collaboration with generative AI company Alchemiq