Brown University researchers found new evidence that asteroids could have brought water to Earth — and they could also bring it to other planets.

Impact experiment setup.

A) A Mylar tray filled with heat-treated powdered pumice. B) Tray centered beneath the impact point. C) The same view as (B) but showing a frame 761.5 milliseconds (μs) after impact. The Mylar has ruptured, directing most of the luminous melt downward into the well for recovery. White lines mark the extent of the glowing plume; the region outlined in gray contains abundant luminous melt.
Image credits R. Terik Daly, Peter H. Schultz, 2018, Planetary Sciences.


In an effort to understand how the blue planet got all its blue (water), researchers at Brown University have turned to NASA and one of its biggest gun rooms.

Their what now?

Exactly how planets got all their water is still open to debate. Compounding the problem is the fact that traces of water were also found in comparatively dry places, such as the Moon’s mantle — dismissing ‘that’s just how the Earth rolls’ as a valid explanation. One possible explanation is that asteroids brought all this water here in the planet’s early days.

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However, this theory never fared that well in the face of computer simulations.

“Impact models tell us that [asteroids] should completely devolatilize at many of the impact speeds common in the solar system, meaning all the water they contain just boils off in the heat of the impact,” says study co-author Peter Schultz, a professor in Brown’s Department of Earth, Environmental and Planetary Sciences, said in a statement.

“But nature has a tendency to be more interesting than our models, which is why we need to do experiments.”

In order to test the validity of this claim with as little computer simulations as possible, the team asked NASA for permission to use their Vertical Gun Range, housed at the Ames Research Center in California. The indoor ballistic facility was built during the 1960s when, NASA needed to see what happens during high-speed cosmic collisions, without having the luxury of powerful computers.

In lieu of real asteroids, the team used marble-sized cylinders of antigorite, a green mineral common in the oceanic crust that contains some 13% water by weight. A tray of dried, powdered pumice stone was used as a target, to simulate the loose layer of dusty minerals covering Earth’s bedrock, according to the authors. A plastic-lined well was affixed beneath this tray to capture the debris left by the simulated asteroid impact.

The team performed several trials, shooting the fake asteroids into the fake Earth at speeds in excess of 11,200 mph, which they write is “comparable to the median impact speed” in the asteroid belt. They report that on impact, some of the pumice stone melted, then quickly re-solidified, forming glass. Pieces of antigorite also got mixed in with the powder and formed breccia, a type of rock formed when bits of preexisting material get cemented together.

The surprising bit, however, was the water content in the debris. Lab analyses revealed that up to 30% of the mock asteroid’s water found its way into the debris left over in the tray — much more than models suggested was possible up to now. The findings lend weight to the theory that asteroids could have brought water to Earth from the depths of the universe.

“These new experiments raise the possibility that growing terrestrial planets trap water in their interiors as they grow,” the researchers wrote.

That being said, there is also evidence in support of Earth generating its own water, through geological processes. The truth is likely somewhere in the middle, but at this point, we can’t say for sure.

The paper “The delivery of water by impacts from planetary accretion to present” has been published in the journal Planetary Science.