High-powered Laser Experiments Provide Insight Into Super-Earth Cores

Posted: Apr 26 2018, 4:01pm CDT | by , Updated: Apr 27 2018, 12:46am CDT, in News | Latest Science News

High-powered Laser Experiments Provide Insight into Super-Earth Cores
Credit: Laboratory for Laser Energetics

Iron alloys under ultrahigh pressure represent the interior structure of large, rocky exoplanets

By using high-powered laser beams, researchers have simulated the extreme conditions beneath the surface of super-Earths. This may lead to better understanding of nature and the composition of super-Earths and their cores.

Super-Earths are rocky exoplanets that are larger than Earth but smaller than the gas giant of our solar system Neptune. To date, more than 2000 super-Earths have been detected in the known universe. But researchers cannot reach these exoplanets directly with instruments because their interior pressures can be extremely intense. Furthermore, we still don’t have direct measurements of our own planetary core which could otherwise be used as a baseline to determine the structure and composition of super-Earths.

"We now have a technique that allows us to directly access the extreme pressures of the deep interiors of exoplanets and measure important properties," said Thomas Duffy from Princeton University. "Previously, scientists were restricted to either theoretical calculations or long extrapolations of low-pressure data. The ability to perform direct experiments allows us to test theoretical results and provides a much higher degree of confidence in our models for how materials behave under these extreme conditions."

In the experiment, researchers compressed two samples of iron for only a few billionths of a second by using a pulse of bright X-rays. One sample was alloyed with 7 weight-percent silicon, similar to the modeled composition of Earth's core while other was mixed with 15 weight percent silicon, a composition that is possible in exoplanetary cores. The resulting diffraction allowed researchers to understand the density and crystal structure of the alloys, which replicate super-Earth cores.

The pressures achieved in the experiment were up to 1,314 gigapascals (GPa), which are about three times higher than previous experiments. This is well beyond the range of conventional experimental techniques such as diamond anvil cells.

"Our approach is newer, and many people in the community are not as familiar with it yet, but we have shown in this (and past) work that we can routinely reach pressures above 1,000 GPa or more (albeit only for a fraction of a second). Our ability to combine this very high pressure with X-ray diffraction to obtain structural information provides us with a novel tool for exploring planetary interiors.” Duffy said.

Researchers found that at ultrahigh pressures, the lower-silicon alloy created its crystal structure in a hexagonal close-packed structure whereas a body-centered cubic packing was observed in the higher-silicon alloy. This suggests the crystal structure changes with higher silicon content.

"Knowledge of the crystal structure is the most fundamental piece of information about the material making up the interior of a planet, as all other physical and chemical properties follow from the crystal structure.” June Wicks from Princeton University said.

Researchers also found that at the highest pressures, the iron-silicon alloys reach 17 to 18 grams per cubic centimeter and become as dense as gold or platinum at Earth's surface. The study is the first to calculate the density and pressure distribution inside super-Earths by taking into account the presence of silicon in the core.

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.




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