Ancient Mars impacts created tornado-like winds that scoured surface

Brown University geologist Peter Schultz observed sets of strange bright streaks coming from a few large-impact craters on the planet’s surface. The streaks are strange because they extend much farther from the craters than normal ejecta patterns, and they are only visible in thermal infrared images taken during the Martian night. Using geological observation, laboratory impact experiments and computer modeling, Schultz and Brown graduate student Stephanie Quintana have offered a new explanation for how those streaks were formed. They show that tornado-like wind vortices created by crater-forming impacts and swirling at 500 miles per hour or more, scoured the surface and blasted away dust and small rocks to expose the blockier surfaces beneath.

Schultz states he first saw the streaks during one of his ‘exploration of Mars’. In his downtime between projects, he pulls up random images from NASA’s orbital spacecraft just to see if he might observe anything interesting. In this scenario, he was looking at infrared images which capture contrasts in heat retention on the surface. Brighter regions at night indicate surfaces that retain more heat from the previous day than surrounding surfaces, just as grassy fields cool off at night while buildings in the city remain warmer.

Schultz’s experiments showed that vapor plumes travel outward from an impact point, just above the impact surface, at incredible speeds. Scaling laboratory impacts to the size of those on Mars, a vapor plume’s speed would be supersonic. And it would interact with the Martian atmosphere to generate powerful winds. Schultz and Quintana showed that the streaks are nearly always seen in conjunction with raised surface features. As the plume raced outward from the larger impact, it encountered the small crater rim, leaving bright twin streaks on the downwind side.

The researchers’ experiments show that the presence of volatile compounds, a thick layer of water ice on the surface or subsurface, affect the vapor amount that rushes out from an impact. The streaks now can serve as indicators of whether ice may have been present at the time of an impact, which could lend insight into reconstructions of past climate on Mars. Equally possible, the streaks could be related to the composition of the impactor, such as rare collisions by high-volatile objects, such as comets.


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