By Will Dunham
WASHINGTON (Reuters) – Seismic waves sparked by a meteorite impact on the far side of Mars have offered fresh insights into the planet’s deep interior, leading scientists to reconsider the structure of Earth’s neighboring world.
The recent seismic data suggests the presence of a previously unknown layer of molten rock surrounding a smaller, denser liquid metallic core at the center of Mars. These findings, published on Wednesday, have been made possible by the seismic measurements captured by NASA’s InSight lander.
Seismic waves produced by earthquakes, including those caused by meteorite impacts, exhibit different speeds and shapes as they travel through various materials within a planet. InSight’s seismometer instrument has provided crucial information about the internal structure of Mars.
A meteorite impact occurred on September 18, 2021, in Tempe Terra, a highland region of Mars. This impact triggered a magnitude 4.2 earthquake and left a crater measuring approximately 425 feet (130 meters) in width. Significantly, it took place on the opposite side of Mars from InSight’s location in a plains region called Elysium Planitia.
Amir Khan, a planetary scientist from ETH Zürich in Switzerland and lead author of one of the scientific papers published in the journal Nature, emphasized the significance of this far side impact. Khan stated, “Previously, we had not observed any seismic waves that had transited the core. We had only seen reflections from the top of the core.”
Analysis of the seismic waves indicates that previous understanding of the Martian interior was incomplete. Scientists have discovered the presence of a molten silicate layer approximately 90 miles (150 km) thick surrounding the core. This molten region is located at the bottom of the mantle, which refers to the interior portion of Mars.
Additionally, the researchers have reevaluated the size of the core. They determined that it has a diameter of around 2,080 miles (3,350 km), making it about 30% smaller in volume than previously estimated.
The mantle, a rocky layer situated between the planet’s outermost crust and core, extends about 1,055 miles (1,700 km) beneath the surface. Unlike Mars, Earth does not possess a molten layer around its core. One of the studies indicates that the Martian layer is entirely molten, while the other suggests it is mostly molten, with the upper part partially molten.
Henri Samuel, lead author of the second study and a planetary scientist working at Institut de Physique du Globe de Paris, explained, “The molten and partially molten layer is essentially composed of silicates (rock-forming minerals) that are enriched in iron and in radioactive heat-producing elements compared to the overlying solid mantle.”
The Martian core mainly consists of iron and nickel, but it also contains lighter elements like sulfur, oxygen, carbon, and hydrogen. The researchers’ analysis indicates that these lighter elements make up about 9-15% of the core’s composition by weight, which is lower than previous estimates.
Mars, the fourth planet from the sun, has a diameter of approximately 4,220 miles (6,791 km), while Earth’s diameter is about 7,926 miles (12,755 km). In terms of total volume, Earth is nearly seven times larger.
In 2022, NASA retired InSight after four years of operation.
“The InSight mission has provided us with valuable insights into Mars through its unique seismic record,” said Samuel. “Planets are complex systems where various processes occur on different spatial and temporal scales, and Mars is no exception.”
(Reporting by Will Dunham; Editing by Daniel Wallis)
