WASHINGTON (Reuters) – Seismic waves generated by a meteorite impact on the far side of Mars where NASA’s InSight lander is resting have provided new clues about the red planet’s deep interior, prompting scientists to reevaluate the anatomy of the Earth-bound planet.
New seismic data suggests a heretofore unknown layer of molten rock surrounds the liquid metal core — the planet’s innermost component — and is smaller and denser than previously estimated, researchers said Wednesday.
Waves from earthquakes — including those from meteorite impacts — vary in speed and shape as they travel through different materials within the planet. Data from InSight’s seismic instrument allowed us to focus on the planet’s internal structure.
A meteorite impact that occurred in a Martian highland region called Tempe Terra on September 18, 2021, caused a 4.2-magnitude earthquake and left a crater about 425 feet (130 meters) wide. It happened on the other side of Mars from InSight’s site in a plains region called Elysium Planitia.
“The importance of the far-side impact is that it produces seismic waves that pass through the deep interior of the planet, including the planet’s core. Previously, we did not observe any seismic waves that crossed the planet’s core. We only saw reflections from the top of the planet.” Planetary scientist Amir Khan of ETH Zurich in Switzerland, lead author of one of two scientific papers on the new findings published in the journal, said: nature.
The behavior of the waves indicated that previous assessments of Mars’ interior were missing something: the presence of a molten silicate layer about 90 miles (150 km) thick surrounding the core. This molten region is located at the bottom of the planet’s interior called the mantle.
The researchers also recalculated the size of the core, finding that its diameter is about 2,080 miles (3,350 kilometers), and its size is about 30% smaller than previously thought.
The mantle – a rocky layer located between the planet’s outer crust and the planet’s core – extends about 1,055 miles (1,700 kilometers) below the surface, the researchers said. Unlike Mars, Earth does not have a molten layer around its core. One of the two studies published on Wednesday indicates that this layer is completely molten, while the other indicates that most of it is completely molten, and the upper part is partially molten.
“The molten and partially molten layer consists mainly of silicates (rock-forming minerals) enriched in iron and heat-producing radioactive elements compared to the solid mantle that covers it,” said Henri Samuel, a planetary scientist at the French National Center for Research. CNRS works at the Institute of Physics at the Globe de Paris and is the lead author of Second study.
The core of Mars is mostly iron and nickel, but it also contains some lighter elements such as sulfur, oxygen, carbon and hydrogen. The researchers concluded that these lighter elements constitute about 9-15% of the composition of the nucleus by weight, which is less than previously estimated.
“This amount of light elements is no different from that found in the Earth’s core, which is estimated at about 10%,” Khan said.
The diameter of Mars, the fourth planet from the sun, is about 4,220 miles (6,791 km), compared to the diameter of Earth, which is about 7,926 miles (12,755 km). Earth is about seven times larger in total volume.
NASA retired InSight in 2022 after four years of operation.
“We have learned a lot about Mars by studying the unique seismic record provided by the InSight mission,” Samuel said. “The planets are rich and complex systems because they are places where many different types of processes coexist and behave on different spatial and temporal scales, and Mars is no exception.”
Will Dunham reports. Edited by Daniel Wallis
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