US, WASHINGTON (ORDO NEWS) — Terrestrial experiments on iron-sulfur alloys, which are believed to make up the core of Mars, for the first time reveal the details of the seismic properties of the planet. This information will be compared with the observations made by space probes on Mars in the near future. Whether the results coincide between experiment and observation, or they do not confirm existing theories about the composition of Mars, or cast doubt on the history of its origin.
Mars is one of our closest neighbors, but it is still very far – from 55 to 400 million kilometers, depending on where the Earth and Mars are relative to the Sun. At the time of writing, Mars was at a distance of about 200 million kilometers, and in any case, getting to it is extremely difficult, expensive, and dangerous. For these reasons, it is sometimes more sensible to explore the red planet using simulations here on Earth than send an expensive space probe or, in the future, people.
Keisuke Nishida, Assistant Professor, Department of Earth and Planet Science, University of Tokyo, and his team study the internal work and composition of Mars using seismic data that show not only the current state of the planet, but also offer its past, including its origin.
“The study of the deep bowels of the Earth, Mars and other planets is one of the great frontiers in science,” Nishida said. “This is charming, partly because of its sheer scale, and also because of how we safely explore them from the surface of the Earth.”
For a long time it was believed that the core of Mars probably consists of an alloy of iron and sulfur. But given how inaccessible the earth’s core is to us, direct observations of the core of Mars will probably have to be postponed for some time. This is why seismic detail is so important because seismic waves, akin to extremely powerful sound waves, can travel through the planet and offer a glimpse inside, albeit with some reservations.
“The NASA Insight probe is already on Mars and is collecting seismic readings,” Nishida said. “However, even with seismic data, there was an important missing piece of information without which this data could not be interpreted. We needed to know the seismic properties of the iron-sulfur alloy, which was believed to be the core of Mars.”
Nishida and the team now measured the speed of what is known as P-waves (one of two types of seismic waves, the other S-waves) in molten iron-sulfur alloys.
“Due to technical difficulties, it took us more than three years to be able to collect the ultrasound data we needed, so I am very glad that we have them,” Nishida said. “The sample is very small, which may surprise some people, given the enormous scale of the planet that we are effectively modeling. But micro-scale high-pressure experiments help investigate macro-scale structures and the long history of planetary evolution.”
A molten alloy of iron and sulfur just above its melting point of 1500 degrees Celsius and subjected to 13 gigapascals of pressure has a P-wave speed of 4680 meters per second; this is more than 13 times the speed of sound in air, which is 343 meters per second. The researchers used a device called a Kawai multianvil-type press to compress the sample to such pressures. They used X-rays from two synchrotron installations, KEK-PF and SPring-8, to take pictures of the samples and then calculate the P-wave values.
“Using our results, researchers can now determine whether the core is predominantly an iron-sulfur alloy or not,” Nishida said. “If it is not, it will tell us something about the origin of Mars. For example, if the core of Mars includes silicon and oxygen, this suggests that, like the Earth, Mars experienced a huge shock event when it formed. I think we’ll find out.”
The study is published in Nature Communications.
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