Data from the Chinese rover Zhurong is adding to the pile of evidence for oceans on ancient Mars. For a year, this little craft traveled over nearly two kilometers of the Martian surface and made radar scans of buried natural structures that look like ocean shorelines.<\/p>\n
<\/p>\n Zhurong\u2019s ground-penetrating radar (GPR) looked under the surface to a depth of 80 meters. There, the radar instrument found thick layers of material similar to beach deposits on Earth. The best way to create such formations is by wave action stirring up and depositing sediments along the shore of an ocean. If these findings stand, they\u2019ll provide a deeper look into Mars\u2019s ancient warm, wet past, and the existence of long-gone seas.<\/p>\n \u201cThe southern Utopia Planitia, where Zhurong landed on May 15, 2021, is one of the largest impact basins on Mars and has long been hypothesized to have once contained an ancient ocean,\u201d said Hai Liu, a professor with the School of Civil Engineering and Transportation at Guangzhou University and a core member of the science team for the Tianwen-1 mission, which included China\u2019s first Mars rover, Zhurong. \u201cStudying this area provides a unique opportunity to investigate whether large bodies of water ever existed in Mars\u2019 northern lowlands and to understand the planet\u2019s climate history.\u201d<\/p>\n At first, scientists considered lava flows or dunes to explain the structures Zhurong measured. But, their shapes say otherwise. \u201cThe structures don\u2019t look like sand dunes. They don\u2019t look like an impact crater. They don\u2019t look like lava flows. That\u2019s when we started thinking about oceans,\u201d said Michael Manga, a University of California, Berkeley, professor of earth and planetary science. He was part of Hai\u2019s team that recently published a paper about Zhurong\u2019s findings. \u201cThe orientation of these features are parallel to what the old shoreline would have been. They have both the right orientation and the right slope to support the idea that there was an ocean for a long period of time to accumulate the sand-like beach.\u201d<\/p>\n Aside from their meteorological and geological value, the presence of these shoreline structures also implies that Mars\u2019s ancient oceans were ice-free. \u201cTo make ripples by waves, you need to have an ice-free lake. Now we\u2019re saying we have an ice-free ocean. And rather than ripples, we\u2019re seeing beaches,\u201d Manga said. That tells us Mars was a warmer world\u2014at least for a while. Rivers could well have flowed across the surface, contributing rocks and sediments along the shorelines. And, of course, there are structures that imply the presence of oceans. On Earth, oceans provide life habitats and there\u2019s no reason to think that Mars oceans couldn\u2019t have done that, too.<\/p>\n \u201cThe presence of these deposits requires that a good swath of the planet, at least, was hydrologically active for a prolonged period in order to provide this growing shoreline with water, sediment, and potentially nutrients,\u201d said co-author Benjamin Cardenas, an assistant professor of geosciences at The Pennsylvania State University (Penn State). \u201cShorelines are great locations to look for evidence of past life. It\u2019s thought that the earliest life on Earth began at locations like this, near the interface of air and shallow water.\u201d<\/p>\n As far back as Viking, scientists had images showing what looked like irregular shorelines and flow features on the surface. Those features implied bodies of water and flowing rivers. Other missions returned images and data showing ponded areas where smaller bodies of water existed. More recent missions returned images of regions scoured and changed by catastrophic floods. The shoreline features imply that oceans existed.<\/p>\n We know today that Mars\u2019s surface no longer hosts bodies of water. In the past, much of it escaped to space along with Mars\u2019 atmosphere. But some water also went underground and remains there as ice deposits. And, some combined with rocks to form new minerals. Other geological features seem to point to the existence of Martian oceans, like the shorelines Zhurong and Viking measured.<\/p>\n However, the irregular shape of those shorelines continued to intrigue planetary scientists. That\u2019s because they didn\u2019t exactly look like shorelines like we see along Earth\u2019s oceans, which are level. In 2007, Manga came up with the idea that the shapes of the shorelines were altered by changes in the planet\u2019s rotation. Why did that happen? Blame it on volcanoes in the Tharsis region. Some 4 billion years ago volcanic activity there built up a huge bulge. That eventually messed with the planet\u2019s rotation. \u201cBecause the spin axis of Mars has changed, the shape of Mars has changed. And so what used to be flat is no longer flat,\u201d Manga explained.<\/p>\n If the findings hold up, the buried shorelines tell a compelling story of the last days of oceans on Mars. Based on the team\u2019s paper, that water appears to have lasted tens of millions of years. As it disappeared and the climate dried up, wind-blown regolith covered the shorelines that Zhurong measured.<\/p>\n For now, the Zhurong data provides a look into shoreline deposits that are pristine\u2014but buried under the subsurface. \u201cThere has been a lot of shoreline work done,\u201d said Cardenas, \u201cbut it\u2019s always a challenge to know how the last 3.5 billion years of erosion on Mars might have altered or completely erased evidence of an ocean. But not with these deposits. This is a very unique dataset.\u201d<\/p>\n Ancient Beaches Testify to Long-ago Ocean on MarsFiguring Out Mars Shorelines<\/h3>\n
Digging into the Past<\/h3>\n
Shoreline Evidence for Changes on Mars<\/h3>\n
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