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Edge of Mars’ great dichotomy eroded back by hundreds of kilometers

20 January 2025 at 22:14

For decades, we have been imaging the surface of Mars with ever-finer resolution, cataloging a huge range of features on its surface, studying their composition, and, in a few cases, dispatching rovers to make on-the-ground readings. But a catalog of what's present on Mars doesn't give us answers to what's often the key question: how did a given feature get there? In fact, even with all the data we have available, there are a number of major bits of Martian geography that have produced major academic arguments that have yet to be resolved.

In Monday's issue of Nature Geoscience, a team of UK-based researchers tackle a big one: Mars' dichotomy, the somewhat nebulous boundary between its relatively elevated southern half, and the low basin that occupies its northern hemisphere, a feature that some have proposed also served as an ancient shoreline. The new work suggests that the edge of the dichotomy was eroded back by hundreds of kilometers during the time when an ocean might have occupied Mars' northern hemisphere.

Close to the edge

To view the Martian dichotomy, all you need to do is color-code a relief map of the Martian surface, something that NASA has conveniently done for us. Barring a couple of enormous basins, the entire southern hemisphere of the red planet is elevated by a kilometer or more, and sits atop a far thicker crust. With the exception of the volcanic Tharsis region the boundary between these two areas runs roughly along the equator.

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Β© NASA/JPL-Caltech/Univ. of Arizona

Can walls of oysters protect shores against hurricanes? Darpa wants to know.

On October 10, 2018, Tyndall Air Force Base on the Gulf of Mexicoβ€”a pillar of American air superiorityβ€”found itself under aerial attack. Hurricane Michael, first spotted as a Category 2 storm off the Florida coast, unexpectedly hulked up to a Category 5. Sustained winds of 155 miles per hour whipped into the base, flinging power poles, flipping F-22s, and totaling more than 200 buildings. The sole saving grace: Despite sitting on a peninsula, Tyndall avoided flood damage. Michael’s 9- to 14-foot storm surge swamped other parts of Florida. Tyndall’s main defense was luck.

That $5 billion disaster at Tyndall was just one of a mounting number of extreme-weather events that convinced the US Department of Defense that it needed new ideas to protect the 1,700 coastal bases it’s responsible for globally. As hurricanes Helene and Milton have just shown, beachfront residents face compounding threats from climate change, and the Pentagon is no exception. Rising oceans are chewing away the shore. Stronger storms are more capable of flooding land.

In response, Tyndall will later this month test a new way to protect shorelines from intensified waves and storm surges: a prototype artificial reef, designed by a team led by Rutgers University scientists. The 50-meter-wide array, made up of three chevron-shaped structures each weighing about 46,000 pounds, can take 70 percent of the oomph out of waves, according to tests. But this isn’t your grandaddy’s seawall. It’s specifically designed to be colonized by oysters, some of nature’s most effective wave-killers.

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Β© Kemter/Getty Images

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