Mars

An inspiration for many sci-fi stories, and the most visited planet in the Solar system. Learn more about the red planet here!

Formation

After the Sun ignited hydrogen and began to supply energy to the Solar System, space around the Sun was immediately showered by a pressure wave of radiation, pushing the lighter gas and dust far out into the Solar System. Heavier rocky material was not affected, and over time collided to form larger planetesimals. These planetesimals fuel the planets’ formation as they fall under the gravitational pull of the increasing planetary mass, eventually forming Mars.

Composition

Mars is like the other terrestrial planets in structure. A molten core made of nickel and iron is about half the size of the planet, followed by a silicate mantle layer up to the crust. On average the crust on Mars is thicker than the Earth’s crust. Mars is the only other planet besides Earth that is geologically active with Marsquakes, analogous to earthquakes, measured across the surface.

Surface

The surface of Mars is unique through the separation between the smooth Northern hemisphere and the cratered Southern hemisphere. Known as the Martian dichotomy, scientists believe that a large Pluto-sized object smashed into the surface of Mars long ago causing a giant impact crater leading to the discrepancy in the hemisphere surfaces. This leads to an average crust thickness in the Northern hemisphere to be 20 miles, while in the South the average crust thickness is 36 miles. An average elevation difference of 1 mile also occurs between the two hemispheres. The surface is impacted by craters, most of them from the late heavy bombardment. Mars contains extreme surface features, with Olympus Mons being the largest mountain in the Solar System, and Valles Marineris being the deepest and longest canyon in the Solar System. Just like the Earth, Mars has two polar ice caps, but unlike Earth they are composed of dry ice instead of water ice.

Atmosphere

Mars has a thin atmosphere composed of 96% carbon dioxide, and roughly 2% argon and nitrogen each. The pressure from the Martian atmosphere is less than 1% of Earth’s atmosphere, with most of the atmosphere being stripped away due to Solar radiation since Mars does not have a magnetic field to protect the trapped gas unlike the Earth.

Magnetic Field

Mars does not have a magnetic field, but research suggests that it may have had one right after formation. The Southern hemisphere of Mars has a significant portion of its surface composed of residually magnetized material, leftover from the early Martian magnetic field. In contrast, the Northern hemisphere does not have this residual magnetization present in the material, furthering the Martian dichotomy.

Satellites

Mars has had the most spacecraft visit in the Solar System. Starting with Mariner 4, the Martian surface was photographed for the first time, marking the first planet’s surface to be photographed from a satellite. Mariner 6 and Mariner 7 were launched to Mars as a duel mission, taking pictures of the equatorial region and the southern pole region of Mars respectively. Mariner 9 was the first orbiter of Mars, and was able to complete a global mapping of the surface. Within the map large volcanoes and a massive canyon was discovered, along with what appeared to be dry, ancient riverbeds. The two moons of Mars were also examined by Mariner 9.

The first landers on Mars were the Viking 1 and Viking 2 missions. Launched as both a lander and an orbiter for each Viking mission, these were the first landers to successfully take photos on the surface of another planet. These missions were designed to discover biological life on the surface, and took samples from the Martian soil. The results were surprising as unexpected chemical activity was discovered, but no life was discovered. The orbiters were able to map the surface of Mars in more detail and study features on a smaller scale than previously able with the Mariner missions.

Mars Pathfinder contained the first rover to roam another planet. The rover, Sojourner, was able to land on Mars thanks to an innovative new parachute and airbag inventions which slowed the rover down as the spacecraft went through the atmosphere and landed. The rover was able to observe the surface and found rounded pebbles indicative of terrain once shaped by flowing water. Atmospheric conditions on Mars were observed, leading to the discovery of dust devils and thin water ice clouds.

Mars Global Surveyor was a satellite inserted into orbit in order to study the changing surface of Mars over many Martian years. From this information Mars was shown to have predictable seasonal weather patterns, with seasonal dust storms occurring within weeks at the same time period each year. The southern Martian dry ice cap was also shown to be receding, along with the first detailed mapping of the northern Martian dry ice cap. Layered temperature readings of the atmosphere were determined, along with better determination of the interior of Mars thanks to the gravitational effects of Mars on the spacecraft.

Mars Odyssey is the longest lasting Mars spacecraft mission, now operating for over twenty years. Equipped with instrumentation to measure the chemical composition of Mars, the satellite mapped underground water ice over the Surface of Mars. Odyssey was also able to determine the low orbit radiation for Mars is twice that of Earth’s low orbit radiation.

Mars Express is the first satellite to visit another planet in the Solar System for the European Space Agency. Express carries a radar imager designed to detect deep underground pockets of water ice, and the ability to detect the geology of the Martian surface. From this glacial activity and volcanism have been detected.

The twin Mars Exploration Rovers, Spirit and Opportunity, are the most successful rovers that have visited another planet to date. These rovers were sent to sites once believed to have water, containing instruments that could bore into the Martian surface and chemical analyzers to help determine the composition of Martian rocks and soil. Spirit was able to last 6 years before lost communication, while Opportunity lasted 15 years before losing communication, travelling a distance of over 28 miles, the only rover to complete a marathon on another world.

The Mars Science Laboratory, nicknamed Curiosity, is the first of the next generation of rovers sent to Mars. Around the size of a standard SUV, Curiosity is powered by a plutonium generator freeing the rover from limitations of solar power encountered by Spirit and Opportunity. The laboratory on Curiosity includes 10 science instruments ranging from cameras and spectrometers, to lasers and drill bits to analyze soil composition. Curiosity was sent to determine if Mars once contained an environment suitable for life, discovering chemical and mineral evidence when it landed in Gale crater. Curiosity is still roving on Mars today, collecting valuable data.

The best camera ever sent on a satellite was installed on the Mars Reconnaissance Orbiter. The detail on this camera can capture objects as small as a dinner plate on the surface of Mars, paving the way for future landing sites to have detailed identifications of hazardous objects. An instrument to detect subsurface water is included as well.

MAVEN was the first satellite to directly measure the Martian atmosphere, with the goal to detect long-term changes to the composition and density of the atmosphere. Since Mars once held water on the surface, the atmosphere must have been thick enough at one point to sustain the water on the surface. MAVEN can learn how Mars lost density in the atmosphere and subsequently created the environment that is currently viewed on Mars today.

The next large rover to land on Mars following Curiosity is the Mars 2020 mission, Perseverance. This mission will search for evidence of Martian life, something not directly done since the Viking landers five decades prior. Perseverance will also collect canisters of Martian soil to leave on the surface of Mars, collected by a later mission to ultimately be sent back to Earth to utilize instruments not available on the Martian rovers. A drone was included in the Perseverance payload and performed the first flight on a surface of another planet, allowing for future missions to move through the air reaching further targets from the landing site. At the start of its mission, the Mars 2020 rover will be sure to have significant data collection in the following years.