Combining Neutrons and X-Ray Imaging, NIST Scientists Study Meteorites to Explore Mystery of How Earth Acquired Its Water
Color-coded X-ray image of a slice of the meteorite GRA 06100 overlaid with a neutron image of the same slice shows iron-rich material (pink), regions with low concentrations of hydrogen-bearing compounds (green), regions with high concentrations of hydrogen-bearing compounds (blue) and iron-rich hydrogenated compounds (purple). Scale bar is one centimeter. Credit: A. Treiman/Lunar and Planetary Institute/USRA

meteorites are left over from the formation of the solar system and deliver minerals, metals and water to the planet. Analyzing the crevices and mineral-rich deposits inside meteorites can give clues about how the young Earth acquired water and other ingredients essential for life.

Researchers at theNIST have combined two techniques to peer inside rocky remnants.

It's ideal for searching for water and other hydrogen-bearing compounds because of the abundance of neutrons. The best way to find deposits of heavy elements, such as iron and nickel, is to use X-rays.

Movie of the meteorite EET 87503 depicts overlay of X-ray and neutron imaging. Purple and orange denote two different classes of iron-rich minerals; green denotes minerals that contain water in their structure. Credit: NIST

Other methods of analyzing the chemical composition of the rocks, which require cutting thin slices of the meteorites, are less harmful to meteorites. The team is one of the first to use the two techniques at the same time.

The scientists looked at two meteorites that were already known to have mineral and water content. One of the rocks, dubbed EET 87503, is a fragment from the surface of a large asteroid but also contains material from a different type of asteroid.

A chondrite is a rock that has not been altered by melting or other processes since the beginning of the solar system. It has a lot of hydrogen-bearing silicates.

Movie of the meteorite GRA 06100 depicts overlay of X-ray and neutron imaging. Red denotes iron-rich compounds; blue denotes hydrogenated compounds, including water. Credit: NIST

In order to create three-dimensional views of the meteorites, NIST researchers Jacob LaManna and Daniel Hussey, along with colleagues from the Lunar and Planetary Institute in Houston, the Oak Ridge National Laboratory in Tennessee, and the University of Chicago, used the X-ray and neutron beams to Tomography is a technique used to create a 3D image. X-ray tomographic scans are used by physicians to look at the human body.

The locations of metal-rich minerals, silicate minerals, water and other compounds in the two meteorites were revealed through the use of the techniques. The chondrite grains within GRA 06100 were identified and characterized by the use of electron microscopes. It's possible to test theories of how water entered the rock and what pathway the liquid took to alter the composition of minerals by using the 3D image.

Water accounts for 70% of Earth's surface, but it's still the subject of a longstanding debate. After our planet's core had formed, some planetary scientists think meteorites and comets delivered the water and building blocks for life. It is thought that Earth was formed 4.5 billion years ago from bits of gas and dust that swaddled the baby sun.

There are two types of water, ordinary water and heavy water. One way to determine if meteorites were a primary source of water is to compare the amount of meteorites in the rocks to the amount of water on and beneath the surface. Some meteorites have been measured but need to be looked at bigger.

These studies can be aided by the images of the X-ray and neutrons. By knowing the location of mineral, metal and water deposits locked inside meteorites, the images could help researchers determine the composition of other compounds in the rocks.

The NIST team used the NIST Center for Neutron Research to conduct their research.

LaManna said that the team plans to use its dual image technique to study meteorites that are not as well known.

Allan H. Treiman is the author of Coordinated Neutron and Xray computed tomography of meteorites. There is a map of 10.1111.

Journal information: Meteoritics and Planetary Science

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