Mars is one of the most fascinating planets in our solar system. It is a close companion of Earth with a similar atmosphere, weather patterns and polar ice caps.
Throughout history it has been observed, studied and featured in culture and the arts. From astronomers to writers, and radio broadcasters, it has captured our imaginations.
Size
Mars is a small planet, larger than only Mercury and slightly more than half the size of Earth. Its equatorial radius is 3,396 kilometers (2,110 miles) and its mean polar radius is 3,379 km (2,100 miles).
The planet has a dense core at its center between 930 and 1,300 miles (1,500 to 2,100 kilometers) in radius, and it surrounds that core with a rocky mantle between 770 and 1,170 miles (1,240 to 1,880 kilometers) thick and a crust made of iron, magnesium, aluminum, calcium, and potassium between 6 and 30 miles (10 to 50 kilometers) deep.
It has hundreds of thousands of impact craters all over its surface. The largest, the Northern Polar Basin-Borealis Basin, is 10,500 km (6,000 miles) across.
Many of the channels and valleys in these craters, and the gullies and erratic peaks found all over Mars, suggest that liquid water may have flowed across the planet’s surface at some point in its history. However, because of the cold, thin atmosphere, it’s unlikely that any liquid water could exist on the surface for very long.
Since its arrival near Mars’ equator in November 2018, NASA’s InSight lander has been studying the planet’s interior. It’s examining how the planet wobbles on its axis, and it’s also measuring marsquakes.
The planetary scientist who led the research, Michael Meyer, says that the mission is revealing important insights about the Red Planet’s internal structure. He says that the core is between 930 and 1,300 miles in diameter, composed of primarily iron and nickel with trace amounts of sulfur.
Other findings from the InSight mission include evidence that the rocky planet’s mantle is between 770 and 1,170 miles wide. This is because the lander was able to see a part of the rocky mantle as it approached Mars’ surface.
Another discovery from InSight is that the Martian moon Phobos has gradually moved closer to the planet, with a gradual inclination toward its equator. As Phobos approaches the planet at a rate of about 2 cm per year, it will eventually either crash into the planet or disintegrate.
Mass
Mars is the second planet from the Sun and the largest planet in the Solar System. Its mass is 6.42 x 1023 kg and its radius is 3.389 km. It has a density of 3.93 g/cm3.
The average gravity on Mars is 38% of Earth’s.
Aside from its large size, Mars also boasts several notable features. Among them are its two polar caps, each of which is dominated by water ice, and the planet’s most prominent feature, Olympus Mons.
In addition, the Martian surface has numerous impact craters that were formed when it was struck by other objects. The planet’s surface is dotted with ancient volcanic deposits and highlands that appear to be remnants of old tectonic regions.
These features have a reddish hue due to the presence of iron oxides, which give Mars its signature appearance. It also has a thin atmosphere.
During the past few million years, Mars has had a complex history with many changes to its surface. Those changes included the formation of several large craters, such as Isidis and Hellas.
However, the most notable change may have been a major impact that created the Tharsis basin, which covers 40% of the planet’s surface and is the largest planetary impact structure known to date.
Another important event that happened during the same period is the creation of the first known stable body of water on Mars. This sub-glacial lake sits 1.5 km (0.9 mi) below the southern polar cap and is 20 km (12 mi) wide.
Other notable features of Mars include its two moons, Phobos and Deimos, which are believed to have been captured from the nearby asteroid belt. Moreover, the planet has a dazzling array of surface features, including volcanoes, canyons, and even an underground lake.
Atmosphere
Mars has an atmosphere that is very different from Earth’s. It is a thin, largely carbon dioxide-dominated atmosphere, unlike the nitrogen-rich air of Earth. It also has a low temperature, with temperatures ranging from -100 degrees F in winter to about 20 degrees F in summer, as well as very weak gravity.
Early in the planet’s history, Mars had a thick enough atmosphere to support liquid water on its surface, but for unknown reasons it gradually thinned over time. Today, however, it is still possible to find evidence of frozen water ice on the planet’s surface.
The icy caps of the north and south polar regions are made of carbon dioxide ice and are subject to seasonal changes in size, causing the atmospheric pressure to rise and fall in response. The ice also absorbs sunlight, which causes windstorms that can cover the entire planet in a whirlwind called a dust devil.
Currently, the atmosphere of Mars is composed mainly of 95% carbon dioxide; it also contains 2.8% nitrogen, 2% oxygen, 2% argon, and trace amounts of carbon monoxide and water vapour. Trace amounts of noble gases are present as well, suggesting that the atmosphere was much thicker in the past (noble gases do not react with other elements and stay within the gravitational field of the planet).
As a result of its eccentric orbit, Mars has very little global magnetic field. Therefore, its surface and atmosphere are exposed to a tremendous amount of radiation from the sun, including high-energy ultraviolet rays that can damage organic compounds on the planet’s surface.
This is why scientists can see how the Martian surface changes throughout its year. During the northern hemisphere’s winter, the sun’s rays can cause the ice to freeze and shrink, while in summer the icy caps melt and expand.
The ice caps change their shape in response to these changes in the planet’s temperature and pressure, but their mass remains relatively constant. This makes them important to understanding the climate of Mars.
The varying thicknesses of the ice caps affect the way that water vapor in the atmosphere is trapped or sublimed. During the summertime, the ice is released from the ice cap, and it is then able to enter the upper atmospheric layers. This is known as a convection process.
Surface
Mars is a very different world from Earth in many ways. Its surface is a mix of ancient highlands with craters, and sunken plains riddled with channels that may attest to water flows.
The Red Planet’s surface has been mapped by several astronomers over the years, including Giovanni Virginio Schiaparelli (Italian), Wilhelm Beer and Johann Heinrich Madler of Germany, and Pietro Angelo Secchi of Italy. The Italians were first to describe the canali, which are a series of straight lines that indicate the presence of streams, rivers or lakes on the Red Planet’s surface.
These canali are also a hint of the early days of our Solar System, when Mars was much more like ours. Back then, the planet had a much denser atmosphere and more water–rivers, lakes and flood channels.
As the Red Planet moved away from its star, its axis tilted more and more, allowing for periodic warming periods that allowed water to flow on the planet’s surface. However, due to low atmospheric pressure on the Red Planet, liquid water cannot survive for long.
Scientists have analyzed Mars’s rocks with a variety of instruments, including the Mars Global Surveyor and Mars Odyssey orbiters. Among the major rock-forming minerals observed on the Martian surface include plagioclase, olivine, and low-Ca pyroxene.
Other minerals that have been detected on the Martian surface include hematite and clays, both of which are believed to have formed in water-rich environments. Observations of these minerals on Mars are important for understanding the formation and evolution of the planet’s environment.
In addition, the Martian mantle is chondritic in composition, similar to that of the Earth. However, it is more depleted of chalcophile elements such as W and Hf than the Earth’s mantle. The depletion of these elements was likely caused by the presence of sulfur-rich melts in the core of Mars.
The Martian mantle is mostly composed of iron-magnesium silicates and is about 20 Myr old, indicating that it formed shortly after the formation of the planet’s core. The core is rich in noble gases such as argon and nitrogen, which are essential for the evolution of the planet’s environment.
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