Researchers use a new technique to experiment with what is underneath the super-Earths. In the future, they hope to further analyze more material compositions of exoplanets.
With the new high-powered laser beams, researchers are able to directly experiment on the core of a planet three times larger than Earth and analyze its composition despite the intense pressures inside it.
Similar hands-on experimentation has never done before as scientists were previously limited to using either theoretical calculations or complicated extrapolation of low-pressure data, explains Thomas Duffy, a professor of geosciences at Princeton University.
Habitable Exoplanets
With this new laser beam technique, researchers hope that they can next look into the probability that plate tectonics exist on exoplanets, that these planets can generate a magnetic field, and how these super-Earths process its thermal evolution.
Ultimately, further experiments using the breakthrough device can finally yield the answer to the most crucial question on whether exoplanets are habitable.
Extreme Pressures
To date, there are more than 2,000 super-Earths that were already identified. They are bigger than Earth but not as big as Neptune.
These exoplanets are not analogous to any bodies found in the solar system. Without a distinct model, scientists cannot learn about the actual environment that exists on these super-Earths. Previous studies were limited by the fact that Earth's very own planetary core has yet to be measured for comparison.
The most challenging part is that pressures underneath these exoplanets can reach more than 10 times the pressure at the center of the Earth.
With the omega laser beams, the scientists were able to reach breakthrough pressures amounting to up to 1,314 gigapascals (GPa). Previous experiments using diamond anvil cells rarely achieve more than 300 GPa. In comparison, pressures in Earth's core can amount to up to 360 GPa.
This achievement can be more helpful for future modeling of the interior of larger and rocky exoplanets, explained Duffy in the study published in the journal Science Advances.
Core Of Super-Earths
Duffy explains that Earth's core is made up of iron alloyed consist of about 10 percent of a lighter element. The best candidate for the lighter element is silicon, both for Earth and the exoplanets. The scientists played with these two material compositions in their experiment.
June Wicks, lead researcher for the study, and her team target two iron samples using the high-powered laser beams. One sample is alloyed with 7 weight-percent silicon which is closer to the Earth's composition. The other is alloyed with 15 weight-percent silicon, which is closer to the composition of the exoplanetary inner surface.
The team found that in contact with short but intense laser beams, the first sample organized its crystal structure in a hexagonal close-packed structure.
The second sample, meanwhile, organized its crystal structure similar to a body-centered cubic packing like the one in this video:
The researchers also applied the different amount of pressures into the iron-silicon alloys composition. At the most extreme pressures, the composition reaches 17 to 18 grams per cubic centimeter. This is about 2.5 times compared to the density on the surface of Earth. It is also comparable to the density of gold or platinum at Earth's surface.
The team also found that silicon alloys are less dense than unalloyed iron even after applying high pressures. Hence, they concluded that a planet consisting of a pure iron core is not plausible.
Their next step will be to find the exact composition of the lighter elements that can be found on exoplanets.
For the meantime, the researchers said they achieved an important conclusion into the core composition of super-Earth exoplanets — the first to be considered as the more realistic compositions.
