How Asteroids Can Deliver Water Throughout the Solar System

Credit: Schultz Lab / Brown University

For the study, Daly and Schultz used marble-sized projectiles with a composition similar to carbonaceous chondrites, meteorites derived from ancient, water-rich asteroids. Using the Vertical Gun Range at the NASA Ames Research Center, the projectiles were blasted at a bone-dry target material made of pumice powder at speeds around 5 kilometers per second (more than 11,000 miles per hour). The researchers then analyzed the post-impact debris with an armada of analytical tools, looking for signs of any water trapped within it.

They found that at impact speeds and angles common throughout the solar system, as much as 30 percent of the water indigenous in the impactor was trapped in post-impact debris. Most of that water was trapped in impact melt, rock that’s melted by the heat of the impact and then re-solidifies as it cools, and in impact breccias, rocks made of a mish-mash of impact debris welded together by the heat of the impact.

The research gives some clues about the mechanism through which the water was retained. As parts of the impactor are destroyed by the heat of the collision, a vapor plume forms that includes water that was inside the impactor.

“The impact melt and breccias are forming inside that plume,” Schultz said. “What we’re suggesting is that the water vapor gets ingested into the melts and breccias as they form. So even though the impactor loses its water, some of it is recaptured as the melt rapidly quenches.”

 

Samples of impact glasses created during an impact experiment. In impact experiments, these glasses capture surprisingly large amounts of water delivered by water-rich, asteroid-like impactors.

Credit: Brown University

The findings could have significant implications for understanding the presence of water on Earth. Carbonaceous asteroids are thought to be some of the earliest objects in the solar system — the primordial boulders from which the planets were built. As these water-rich asteroids bashed into the still-forming Earth, it’s possible that a process similar to what Daly and Schultz found enabled water to be incorporated in the planet’s formation process, they say. Such a process could also help explain the presence of water within the Moon’s mantle, as research has suggested that lunar water has an asteroid origin as well.

The work could also explain later water activity in the solar system. Water found on the Moon’s surface in the rays of the crater Tycho could have been derived from the Tycho impactor, Schultz says. Asteroid-derived water might also account for ice deposits detected in the polar regions of Mercury.

“The point is that this gives us a mechanism for how water can stick around after these asteroid impacts,” Schultz said. “And it shows why experiments are so important because this is something that models have missed.”