Mars

Mars is a rocky planet in our solar system, fourth planet from the sun. It is about half the size of Earth, but with a less dense composition than Earth. It is often referred to as the Red Planet because iron oxide at the surface gives it a reddish appearance. Mars has a very thin, rarefied atmosphere compared to Earth. It consists mostly (96%) of carbon dioxide, about 2% argon, 2% nitrogen and some traces of oxygen and water. It is also dusty. Mars’s radius is 3 390 km (about half of Earth’s) but it’s mass is only 11% of Earth’s mass. The average density of Mars is 3.9 g/cm3. There have been many campaigns to study Mars, the first Mariner 4 was a flyby mission. There are currently 5 spacecrafts in orbit and 2 rovers on the surface, the Mars Exploration Rover Opportunity and Mars Science Laboratory Curiosity.

Structure of Mars

As a rocky planet, Mars differentiated after formation into a core, mantle and crust formation we see on other planets, like Earth. The core of Mars has a radius of 1 794 km. It is made of mostly iron and nickel and some ( 16%) sulphur. It appears the core has more lighter elements in it than on Earth. The core is surround by a silicate mantle like on Earth. There is evidence of tectonic and volcanic activity on the surface of Mars, but it appears to no longer be active. The crust of Mars, which retains the evidence of previous tectonic activity, is between 50 and 125 km thick. This means Mars has a much thicker crust than Earth. Because the internal dynamics of Mars are different from Earth, this plays a role in the different crustal thicknesses of the two planets.

Dynamics of Mars

Unlike on Earth, where the surface is actively mobile and being replen- ished, Mars appears to have a dormant surface presently. There is evidence that surface rocks have been magnetized indicating that Mars had a magnetic field in the past, even though it current does not appear to. There is a large canyon on the surface, Valles Marineris, that is about 4000 km long. It is possible that this is a plate boundary, implying Mars was once a planet with two large plates.

Mars also has the largest volcano in the solar system, Olympus Mons, which is not extinct. It is in a region with several other large volcanos. This further supports the idea of an active mantle with a mobile lid in the past.

Video of stagnant lid convection

Here we see a video of mantle convection as it might appear today on Mars. Because there is no longer any tectonic activity on the surface, the planet is currently in a stagnant lid regime, where the mantle convects, but the surface does not subduct into the mantle. The surface is not being replenished with new material, instead it grows thicker over time, as the mantle cools at the surface.