Mars’s surface may be dusty and quiet today, but the inside is a much more turbulent place. Science has published new research that shows the mantle of the Red Planet isn’t the smooth and layered structure you see in textbooks. It’s filled with fragments from the past that are preserved, like an old Rocky Road.
Earth, Mars, and other rocky planets are traditionally pictured as layer cakes. The crust, mantle and core of the planet are stacked together like layers in a shortbread cookie. Mars is a planet that breaks the mold. The interior of Mars is uneven and lumpy.
NASA’s InSight Mission, which tracked seismic activity on Mars detected subtle vibrations moving through the interior of the planet. Scientists from Imperial College London, among others, were led by these “seismic whistles” to discover giant fragments that are up to four kilometers in width, deep inside the Earth’s Mantle. The chunks may be remnants of Mars’s early creation, which have been preserved as geological fossils.
Mars, and other rocky worlds were formed about 4.5 billion ago when dust and rocks orbiting the Sun’s young clumped under gravity. Mars, once it had taken on its current shape, was subjected to a series massive collisions, similar to those that formed the Moon.
The colossal impact released enough energy to create vast magma oceans. These oceans left distinct pieces of material behind as they cooled, crystallized and froze. InSight is now believed to be detecting these fragments.
Mars’ molten core was formed by early collisions that broke up its crust and mantle, and possibly debris from impactors. These varied materials became stuck as Mars cooled. It was not strong enough for the mixing to produce uniformity.
Mars, unlike Earth which recycles mantle and crust through plate tectonics constantly, developed an outer layer very early. It stopped the mixing of its interior and made it into a geological “time capsule”.
Dr Charalambous said, Most of the chaos on Mars likely occurred in its first 100,000,000 years. We can detect the traces of this chaos after 4 and a 1/2 billion years, which shows how slowly Mars’s inner sphere has been moving ever since.
NASA’s InSight Lander recorded data on eight marsquakes. Two of them were the result of recent meteorite impact craters that are about 150 meters in diameter. Scientists noticed that the seismic waves from these quakes traveled through Mars’s Mantle. They also noted something strange: The higher frequency waves arrived at sensors later.
The delay indicates that waves are getting scattered, or that they have slowed, which is indicative of a mantle with an uneven surface or one that has “chunks” rather than a smooth interior.
Dr Charalambous said, These signals displayed clear interference while they traveled through the deep interior of Mars. This is consistent with the presence of a large number of mantles of various compositions that are remnants of Mars’ early history.
What happened on Mars was that the surface of Mars solidified after these early events. It became a static lid. The mantle below was sealed, locking those chaotic ancient features in, as if it were a time capsule on Mars.
Mars’s inner structure has not changed much since the early days. Unlike Earth where the tectonic plate constantly moves and recycles surface material, such as at the Cascadia Subduction Zone, Mars interior is essentially the same. Mars’s mantle is revealed by seismic data: it contains a number of large, 4 km wide fragments surrounded with many smaller fragments.
Professor Tom Pike who, with Dr Charalambous, worked to determine the cause of these pieces, stated: The fractal distribution is what we see when the force of a collision causes an object to be weakened. When a glass shatters on a floor tile, you see the exact same thing as when a meteorite hits a planet. It breaks up into several large shards along with many smaller ones. We can detect the distribution of these shards even today.
Scientists could use this discovery to better understand the evolution of other planets like Venus and Mercury. Mars’s interior is untouched, giving us an opportunity to see the history of planets without active tectonics.
Journal Reference
- Constantinos Charalambous, W. Thomas Pike, Doyeon Kim et al. Seismic evidence of a martian mantle with a high degree of heterogeneity. Science. DOI: 10.1126/science.adk4292
