Lab experiments explore origins of gullies on Asteroid Vesta

Los Angeles CA (SPX) Dec 23, 2024
The rugged surface of asteroid Vesta, studied extensively by NASA's Dawn mission, features craters and mysterious gullies whose formation has puzzled scientists. These deep channels, previously hypothesized to result from debris flows driven by meteoroid impacts and temperature changes, are now thought to involve a surprising factor: brief flows of water.

A recent NASA-funded study, published in the Planetary Science Journal, suggests that meteoroid impacts on Vesta could have melted subsurface brines, resulting in short-lived liquid flows. These flows may have carved gullies and deposited sediment fans, mimicking processes seen on Earth. Laboratory experiments replicated Vesta-like conditions, offering new insights into this phenomenon.

While the existence of frozen brines on Vesta remains unproven, scientists theorize that impacts might expose and melt subsurface ice. The resulting liquid could flow briefly before refreezing, creating features resembling terrestrial landscapes.

"Not only do impacts trigger a flow of liquid on the surface, the liquids are active long enough to create specific surface features," explained Jennifer Scully, planetary scientist and project leader at NASA's Jet Propulsion Laboratory (JPL). "But for how long? Most liquids become unstable quickly on these airless bodies, where the vacuum of space is unyielding."

The study highlights sodium chloride (table salt) as a crucial component. Tests revealed that pure water freezes almost instantly in Vesta-like conditions, while briny liquids remain fluid for over an hour. "That's long enough to form the flow-associated features identified on Vesta, which were estimated to require up to a half-hour," said Michael J. Poston, lead author from the Southwest Research Institute.

The Dawn spacecraft, launched in 2007, spent 14 months orbiting Vesta and nearly four years exploring Ceres before concluding its mission in 2018. Dawn revealed evidence of brine activity on Ceres, suggesting that subsurface reservoirs might still transfer briny liquid to the surface. While the new research focuses on Vesta, it also informs theories about geologic processes on Ceres and other celestial bodies.

Simulating Vesta-like Conditions

Scientists utilized the Dirty Under-vacuum Simulation Testbed for Icy Environments (DUSTIE) at JPL to recreate the low-pressure conditions following a meteoroid impact. By exposing liquid samples to a vacuum, the experiments demonstrated that while pure water froze instantly, salty fluids continued to flow before freezing.

Brine flows, which were tested at depths of a few centimeters, are believed to correspond to larger-scale features on Vesta, potentially tens of yards deep, requiring even more time to refreeze. The experiments also replicated "lids" of frozen material that stabilize underlying liquids, enabling them to flow for extended periods despite vacuum conditions.

This phenomenon parallels lava flows on Earth, where insulated lava tubes allow longer movement compared to exposed lava. Similar mechanisms might explain icy volcanic activity on Europa and potential mud volcanoes on Mars.

"Our results contribute to a growing body of work that uses lab experiments to understand how long liquids last on a variety of worlds," Scully added.

Research Report:Experimental Examination of Brine and Water Lifetimes after Impact on Airless Worlds