- Unusual flow-like features appear on some airless bodies in the solar system, such as Vesta, Ceres and Europa. How did they form in the absence of an atmosphere?
- Temporary flows of briny water may be the answer. A new study showed meteoroid impacts could melt salty ice, allowing it to flow briefly on the surface.
- The flows would last long enough to cause significant erosion such as gullies and landslides, even with no atmosphere.
Does salty water create mysterious flows on airless worlds?
Flowing water produces distinct landscape features such as riverbeds, valleys, mudslides and more. We’ve seen their effects on Earth as well as Mars, where liquid water flowed billions of years ago. A new joint study between the Southwest Research Institute (SwRI) and NASA’s Jet Propulsion Laboratory (JPL) suggests water may also explain mysterious flow-like features on airless dwarf planets, small moons and asteroids. On October 21, 2024, the researchers said the water would have been in the form of temporary salty brines resulting from meteoroid impacts.
The researchers, led by Michael J. Poston at SwRI, published their peer-reviewed findings in The Planetary Science Journal on October 21, 2024.
Mysterious flows on airless worlds
The study focused on bodies in the solar system with known ice in their crusts but very little atmosphere. This included asteroids like Vesta, the dwarf planet Ceres and Jupiter’s moon Europa. They all display features on their surfaces that look like those created by flowing water. But how could that happen on bodies with no atmosphere?
The research team found that water could still be the explanation. But it wouldn’t be pure water. Instead, it would be temporary flows of briny (salty) water. Meteoroid impacts could melt ice in the crust, allowing it to flow briefly on the surface. Project Principal Investigator Jennifer Scully at JPL said:
We wanted to investigate our previously proposed idea that ice underneath the surface of an airless world could be excavated and melted by an impact and then flow along the walls of the impact crater to form distinct surface features.
As the paper stated:
The role played by transient impact-induced endogenous brines in the formation of geomorphic features has been proposed on airless worlds such as Europa, Vesta and Ceres, as well as on worlds with thin atmospheres such as Mars. After liquefaction, the hypothesized brines flow in a debris-flow-like process, incising curvilinear gullies and constructing lobate deposits within newly formed craters.
Flowing water in an airless vacuum
So how long could briny water flow on an airless body? To find out, the researchers simulated the surface conditions of the asteroid Vesta. They wanted to know how much pressure the surface ice experiences when a meteoroid impacts it. And, subsequently, how long could the water remain liquid before re-freezing again.
Poston and his colleagues used a modified test chamber at JPL to rapidly decrease the pressure on a sample of water. A meteoroid impact on Vesta would create a temporary localized atmosphere. The test simulated the sudden drop in pressure as the atmosphere then dissipated. In the experiment, the water immediately expanded as a result and ejected material from the sample chamber.
SwRI and JPL co-led study offers insights into mysterious features on airless worlds
— Southwest Research Institute (@SwRI) October 21, 2024
Salty brines needed
Overall, pure water re-froze too quickly to have much of an effect, but briny water lasted longer. As Poston explained:
Through our simulated impacts, we found that the pure water froze too quickly in a vacuum to effect meaningful change, but salt and water mixtures, or brines, stayed liquid and flowing for a minimum of one hour. This is sufficient for the brine to destabilize slopes on crater walls on rocky bodies, cause erosion and landslides and potentially form other unique geological features found on icy moons.
If the findings are consistent across these dry and airless or thin-atmosphere bodies, it demonstrates that water existed on these worlds in the recent past, indicating water might still be expelled from impacts. There may still be water out there to be found.
Water on other small worlds in the solar system
Scully also led another study, announced back in 2015, of evidence for briny water flows on Vesta. The new work now expands on those previous findings and extends them to other airless bodies like Ceres and Europa.
And just earlier this month, scientist said there is evidence that Ceres might have been a muddy ocean world. Europa, as we now know, is still an ocean world, under its outer icy crust. And it’s just one of several known ocean moons in our solar system. Saturn’s ocean moon Enceladus literally shoots out jets of salty water vapor into space through cracks in its icy surface. So it’s quite possible other small icy and watery bodies in the solar system can still have water on their surfaces, even if only very briefly.
Bottom line: A new study from researchers at SwRI and JPL suggested that briny water could explain unusual flows on airless worlds like Vesta, Ceres and Europa.
Source: Experimental Examination of Brine and Water Lifetimes after Impact on Airless Worlds
Via SwRI
Read more: Flowing water on Vesta?
Read more: Dwarf planet Ceres might have been a muddy ocean world