Layers play an essential part in shaping planet’s history and future development, including their melting effects on mantle material and volcanic eruptions that alter climate, foster life or destroy it.
Scientists are now using the InSight lander to record marsquakes to examine these layers that lie below Mars, hoping that by doing so they will reveal its structure – from its crust and upper mantle down through to its core.
Crust
Mars formed by collecting dust and larger rocks from space as it evolved, eventually amassing an accumulation of material known as its core, with silicate-rich rocks rising up from below as crust and mantle layers. Over time it gradually cooled and heated back up again due to constant bombardment by meteoroids and radioactive decay of elements, leading to its internal structure being reorganized – densest materials sinking toward its center, with silicate-rich rocks rising to form crust and mantle layers and its core becoming separated as separate layers – an effect known as differentiation that caused its separation into three distinct layers: crust, mantle and core.
InSight, currently exploring Mars’ surface, is anticipated to provide a more complete picture of its interior by measuring the size and depth of its crust. InSight seismometer will record two types of seismic waves: P-waves and S-waves. When travelling through Martian crust layers with different densities of rock layers it encounters delays between arrival times of these waves, so InSight seismometer can tell when physical transitions such as from crust to mantle occur.
Scientists have used this technique to compute the average thickness of Mars’ crust. Furthermore, using a new model of its mantle layer beneath, they estimated how far beneath it extended. Based on these calculations, authors of a Science paper estimated that its crust may range between 30 and 72 kilometers thick – or just under half as thick as Earth’s.
Researchers used this same approach to determine whether or not the crust is stratified, which involves layering rocks of differing composition or temperature into layers that protect each other from exposure to heat or radioactivity from the Sun. If stratification occurs, this may help protect deeper layers from being overheated by heat or radiation from outside sources.
The new work could shed new light on Mars’ dichotomy – its striking contrast between flat volcanic lowlands in the northern hemisphere and highland plateaus covered with meteorite craters in its southern half. According to this research, crust thickness seems essentially uniform throughout continent, suggesting that mantle movements may have concentrated different amounts of material into different hemispheres of Martian surface.
Mantle
Mars’ thick layer of dust, known as its mantle, contains basalt – a dark volcanic rock also found on Earth and Luna, rich in magnesium, silicon, sodium and chlorine – as its core. Sulfates and carbonates only form when there’s water present – such as in Columbia Hills where Spirit discovered evidence of lakes long ago – while finely-layered stacks resembling sediments can also be found there.
Sulfates and carbonates on Mars’ surface could be made up of either hydrated minerals, metamorphosed igneous rocks, or debris left from collisions between asteroids and its surface during its first billion years, or contain trace amounts of metals left by them as they hit Mars’s surface. Furthermore, dark areas on its surface could have formed due to interactions between these elements and water.
At shallow depths, the mantle consists primarily of olivine, pyroxenes, and spinel; these minerals make up basalt which is found on Earth, the Moon, Mars, as well as Venus. As one moves deeper down in space, however, its composition changes with increasing core pressure causing Olivine not to remain stable at these pressures and being replaced with high pressure polymorphs such as Wadsleyite or Ringwoodite that possess similar structures but differing compositions.
Scientists still do not fully understand the structure of Mars’ lower mantle, however. What they do know is that it is hot and under intense pressure – which explains why it does not convect like it does on Earth. This lack of convection could have been one reason for why its magnetic field vanished billions of years ago.
Mars’ core is thought to be similar to our own in that it likely contains liquid iron that acts as a protective magnetic field against solar wind abrasion.
Core
Researchers now have a better understanding of Mars’ inner structure thanks to research from InSight’s spacecraft lander, equipped with seismometer. Seismic waves from marsquakes and meteorite impacts were recorded and researchers then measured how long it took for these waves to travel through both core and mantle layers before using this data to build models of their physical properties and create models of Mars’ core’s physical characteristics.
The team, led by Jessica Irving from University of Bristol in England, states their findings suggest the Martian core may be smaller and denser than anticipated, and contains significant proportions of light elements alloyed with iron (such as sulfur). They published these findings in Proceedings of the National Academy of Sciences USA.
To accurately characterize the properties of Earth’s core, the team studied two seismic events generated by marsquakes and meteorite impacts at different locations. By timing wave travel times through both layers of earth’s interior, they could measure time for waves to travel through both layers before using this information to develop models of elastic wave-speed properties of its elastic core and mantle layers.
Researchers used this data to calculate the size and density of Mars’ core, as well as determine its composition – iron predominating but with other light elements present as well. They concluded that its density was lower than Earth’s and suggested stratification within it; an effect which may account for its loss early in its history.
The discovery bolsters the theory that Mars’ layers are formed through geological processes similar to those which formed Earth and its moon, such as erosion. Ice-rich material could have fallen to Earth from space and frozen upon contact before gradually accumulating over time to form smooth layers within craters or along mountain sides – similar to how Earth formed itself over time.
Underneath Mars’ crust lies a vast mantle, stretching 969 miles (1,560 kilometers). Evidence indicates this portion has experienced both tectonic and volcanic activity in its past but now seems dormant. Unlike Earth, Mars doesn’t feature tectonic plates; rock fractures that cause earthquakes occur due to stresses resulting from its slight shrinkage as it cools off.
Surface
NASA’s InSight mission provides us with our first glimpse of Mars’ interior structure. What they have found may have profound ramifications for how we understand its formation and evolution over time.
Mars’ surface consists of a thin rocky layer called the crust, which covers its mantle and core. Scientists speculate that this top layer reflects material deposited during its first billion years due to intense asteroid bombardment. They suspect it is composed predominantly of basalt — an acidic volcanic rock with abundant silicon, oxygen, magnesium, iron and potassium content which gives its red hue.
Beneath Mars’ crust lies a thicker silicate mantle that may have experienced significant tectonic and volcanic activity in its past, yet is likely dormant now. Like Earth, Mars likely features both liquid outer cores and solid inner ones similar to our own; however, with Mars having smaller and denser cores ranging in radius between 1,780-1,810 kilometers than our own core.
Martian surface conditions fall below the triple point of water, making life impossible in liquid form; however, subsurface layers could support extant or ancient forms. Unfortunately, however, Mars’ hostile radiation environment and atmosphere prohibit survival of organic molecules near its surface.
Mars is also remarkable because it lacks plate tectonics – which involves the movement of rigid plates (lithosphere) on an upper mantle with mobile upper mantle material (asthenosphere). Although scientists do not know why this is the case, they know it lacks chains of volcanoes and long ridges characteristic of active tectonism, its core does not rotate as expected from having an active magnetic field, instead scientists suspect its lack of sulphur causes convection to cease convection thus dissolving its magnetic field completely.