Scientists identify layer of molten rock in the deep interior of Mars – 10/25/2023 – Science

Seismic waves generated by the impact of a meteorite on the opposite side of NASA’s InSight module on Mars have provided new clues about the deep interior of the red planet, leading scientists to reevaluate the anatomy of Earth’s planetary neighbor.

The new seismic data indicates the presence of a previously unknown layer of molten rock surrounding a liquid metallic core — the planet’s innermost component — that is smaller and denser than previously estimated, researchers said Wednesday ( 25).

Waves generated by earthquakes — including those caused by meteorite impacts — vary in speed and shape as they pass through different materials within a planet. Data from the InSight robot’s seismometer allowed greater attention to the internal structure of the planet.

The meteorite impact, which occurred in a mountainous Martian region called Tempe Terra, on September 18, 2021, triggered a magnitude 4.2 earthquake and left a crater about 130 meters wide. It occurred, as mentioned previously, on the opposite side of Mars from InSight’s location, which is in a flat region called Elysium Planitia.

“The importance of the impact on the far side was that it produced seismic waves that passed through the deep interior of the planet, including the core. Previously, we had not observed any seismic waves that had passed through the core. We had only seen reflections from the top of the core,” said the planetary scientist Amir Khan, from ETH Zürich, Switzerland, lead author of one of the two scientific articles on the new discoveries published in the journal Nature.

The behavior of the waves indicated that previous assessments of the Martian interior were leaving something out — the presence of a layer of molten silicate about 150 km thick around the core. This molten region is at the bottom of the planet’s inner portion called the mantle.

The researchers also recalculated the size of the nucleus and found that it has a diameter of about 3,350 km, with a volume about 30% smaller than previously thought.

The researchers said the mantle — a rocky layer between the planet’s outer crust and core — extends about 1,700 km below the surface. Unlike Mars, Earth does not have a molten shell around its core. One of two studies published Wednesday indicates that this layer is completely melted, while the other indicates that most of it is completely melted, with the upper portion partially melted.

“The molten and partially molten layer is essentially composed of silicates [minerais formadores de rochas] which are enriched in iron and heat-producing radioactive elements compared to the overlying solid mantle,” said Henri Samuel, a planetary scientist at the CNRS, a French national research organization, working at the Institut de Physique du Globe de Paris and lead author of the second study.

The Martian core is mainly composed of iron and nickel, but it also has some lighter elements such as sulfur, oxygen, carbon and hydrogen. The researchers concluded that these lighter elements make up about 9% to 15% of the core’s composition by weight, less than previously estimated.

“This amount of light elements is no different from that in the Earth’s core, which is estimated to be about 10%,” Khan said.

Mars, the fourth planet from the sun, has a diameter of about 6,791 km. The diameter of the Earth is about 12,755 km. The Earth is almost seven times larger in total volume.

NASA retired InSight in 2022 after four years of operations.

“We’ve learned a lot about Mars by studying the seismic record provided by the InSight mission,” said Samuel. “Planets are rich, complex systems because they are a place where many different types of processes coexist and act on multiple spatial and temporal scales, and Mars is no exception.”