On May 24th, 2016 we learned about

Meteorites may have blasted tsunamis across Mars, as long as there was enough water

There aren’t a lot of explanations for boulders sitting in flat spaces. They’re usually the result of larger objects, like mountains or cliffs, breaking apart, at which point they move down hill. So when fields of bus-sized boulders were found on Mars, scientists started looking at the short list of what could deliver a boulder to an otherwise empty space, based on examples of such arrangements on Earth. The top of that list was tsunamis, which is a bit puzzling since Mars doesn’t have much water, much less oceans, sloshing around anywhere.

Mars didn’t always look this barren though. While we’re very excited about the traces of water we can find today, scientists are fairly certain that Mars used to have plenty of the wet stuff 3.8 billion years ago. A few impact craters then paint a picture where a meteorite hit the planet, creating 400-foot-tall waves that flooded an area 220,000 square miles across. That much movement could have then deposited the boulders far away from their point of origin as rocky monuments to what would have been a devastating event. Actually, it may have been two events, separated by a few million years, as we’ve found more than one crater and boulder field arrangement.

Was there enough water for a wave?

While the physics of this scenario work, some scientists are concerned about the timing. As the Martian atmosphere deteriorated billions of years ago, the planet wouldn’t be able to hold onto heat so well (as there’d be less of a greenhouse effect,) and the water in these tsunami-capable oceans would start evaporating and freezing. This process likely started before the tsunamis would have occurred, meaning the planet-rocking meteorites would have hit an ocean of salty slush rather than liquid. If things were frozen beyond that point, it raises the possibility that the boulders were actually deposited very slowly thanks to the growth and recession of glaciers instead of anything as flashy as a wall of water taller than the Statue of Liberty.

Retorts about runoff

The team behind the tsunami hypothesis doesn’t buy the glaciers though. Beyond the boulders, other geological features point to flow and movement that wouldn’t be consistent with a glacier, and would match a tsunami. They also feel that even an crusty, icy ocean could still make an impressive wave if you slammed a big enough meteorite into it, although the exact physics of that scenario still need to be calculated.

The last missing piece of this story isn’t about the movement of the boulders, but the ocean itself. There are no clear shorelines to mark out where any water once stood, making some of these calculations much trickier to be sure about. However, this may actually support the tsunami hypothesis, as a giant, rushing wave would have done an excellent job of erasing hard edges in the shores, blurring the ocean’s natural boundaries.

Source: Tsunamis on Mars? Splashy Claim Raises Eyebrows. by Nadia Drake, National Geographic

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