Experiment Shows How Asteroids Brought Water To Earth

Rodiano Bonacci
Aprile 26, 2018

"T$3 his gives us a mechanism for how water can stick around after these asteroid impacts", Schultz said.

'It's a process that started while the solar system was forming and continues to operate today'. When Earth was still evolving as a planet, these asteroids regularly hit the planet at high speed. "But nature has a tendency to be more interesting than our models, which is why we need to do experiments".

The source of this water is one of biggest mysteries in understanding, not only the Earth's evolution, but also that of the Moon, Mars, and even the asteroids, says Terik Daly, a planetary scientist now at Johns Hopkins University, in Baltimore, US.

To simulate the carbonaceous chondrites - or chunks of ancient asteroids that may have transported water - the researchers used marble-sized projectiles of a similar composition. The experiment was conducted at the Vertical Gun Range at NASA's Ames Research Center in California, where scientists shot projectiles the size of marbles at targets at a speed of 11,200 miles per hour. According to the measurements they made, the water found on Earth is of similar composition of isotopes, which are atoms of the same chemical element that have a different number of neutrons compared to the original atom of the same element, normally found in carbonaceous asteroids. They then fired these marbles into dry pumice powder at speeds of 5km/s and analysed the post-impact debris for signs of water. When the plume of steam and molten rock cooled down, a lot of the water was preserved in the debris - as much as 30 percent.

Samples of impact glasses created during an impact experiment.

The researchers found that despite the heat, almost 30% of the water was retained.

The question still remains unanswered, but in order to shed some light on the former, the more widely considered theory, a group of scientists, hailing from Brown University in Rhode Island, conducted a series of experiments demonstrating asteroid impacts.

"What we're suggesting is that the water vapor gets ingested into the melts and breccias as they form", Schultz said.

Still, the research team couldn't understand how asteroids brought water to Earth and what was on Earth's surface before that event occurred. Previous research has pointed to icy comets, which would have crashed into a bone-dry Earth and delivered what became our planet's oceans. The mechanism might even explain why traces of water have been observed in the moon's mantle. Water found on the moon's surface in the rays of the crater Tycho could have been derived from the Tycho impactor, Schultz says.

"Impact models tell us that impactors should completely devolatilise at numerous impact speeds common in the solar system, meaning all the water they contain just boils off in the heat of the impact", said Pete Schultz, co-author of the paper. But a new practical experiment shows those computations might have been wrong.

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