Ancient tsunamis reshaped Mars’ landscape

Massive meteorite impacts may have once made waves on the Red Planet. The resulting tsunamis towered nearly as tall as the Great Pyramid of Giza and reshaped the coastline of an ancient Mars’ ocean, researchers propose.

By scrutinizing satellite images of the Martian surface, planetary scientist Alexis Rodriguez and colleagues conclude that tsunamis could have sent water gushing hundreds of kilometers inland and carved the region’s odd geography. Remnants of those tsunami surges could even provide samples of ancient Martian seawater, the researchers report online May 19 in Scientific Reports. The finding lends support to a popular hypothesis that a vast ocean covered Mars’ northern lowlands around 3.4 billion years ago. While other evidence backs up this claim, the ocean’s existence had nonetheless been disputed due to a lack of shoreline features.

“It’s remarkable that as we look closer and longer at the geology of Mars, we see more and more evidence that Mars once had an ocean,” says MIT planetary scientist Taylor Perron, who was not involved in the new work.

Modern Mars is mostly parched, but some scientists speculate that as much as a third of the planet’s surface was once covered in standing bodies of water and ice. Water-carved channels hint that groundwater outbursts flooded Mars’ northern lowlands, forming a colossal ocean larger in area than North America.

The surrounding landscape doesn’t contain any definitive traces of a shoreline, but the area does show evidence that fluids once flowed uphill. After visiting the aftermath of the March 2011 tsunami that devastated Japan, Rodriguez, of the Planetary Science Institute in Tucson, wondered whether walloping waves could have reshaped Mars’ shorelines.

Meteorite impacts large enough to blast out 30-kilometer-wide craters would have hit early Mars every 2.7 million years on average, Rodriguez and colleagues estimate. These impacts could have generated tsunamis up to 120 meters tall that could have flooded as much as 1 million square kilometers of land, an area nearly the size of Texas and California combined.

Studying Mars’ geography, Rodriguez and colleagues identified evidence for at least two sizable tsunamis a few million years apart. The older tsunami pushed boulders as large as double-decker buses into strange places and shifted sediments that obscured the ocean coastlines. The giant wave’s receding waters also carved backwash channels in the Martian surface.

During the millions of years that separated the two events, Mars’ climate chilled, the researchers think. When the second tsunami struck, its ice-rich waters froze before retreating, leaving behind icy bloblike formations. Sampling these formations could allow scientists to glean the chemistry of the ancient ocean, Rodriguez says.

Other processes, such as rapid sea level rise, could have created some of those formations, says Tim Parker, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Still, the new work is “reasonable,” he says, and agrees with his own investigations showing that some Mars’ features could be explained by tsunamis.

Confirming the tsunamis will be tricky, Perron says; no analogous preserved ocean shorelines exist for comparison, even on Earth. Ultimately, an on-the-ground mission might be needed. “It’s an important first step to try and identify these features from orbit,” he says, “but looking at the structures up close would provide a more stringent test.”