Mars, the fourth planet from the Sun and the seventh largest in our solar system, has always captured human imagination. Its striking red color, caused by iron oxide on its surface, makes it one of the most easily recognizable objects in the night sky, appearing as a bright, red dot. This close proximity to Earth and its distinct appearance have placed Mars high on the list of planets scientists wish to explore, with numerous missions already sent and more planned for the future. Writers and filmmakers have also long been intrigued by Mars, often depicting it as a mysterious world, sometimes a hostile planet with Martian invaders, and at other times a new frontier for human colonization.
Mars is the last of the terrestrial planets in the solar system, which include Earth, Venus, and Mercury. Its surface is composed of a variety of geological features, some of which resemble those on Earth, such as impact craters, valleys, sand dunes, polar ice caps, mountains, and canyons. Notably, Mars is home to Olympus Mons, the largest volcano and tallest planetary mountain in the solar system, as well as Valles Marineris, one of the largest canyons known. Although no signs of life have been found on Mars, evidence suggests that it was once much wetter than it is today, raising the possibility that it might have supported life in the distant past.
The name “Mars” is derived from the Roman god of war, a fitting moniker given the planet’s blood-like hue. This reddish appearance has been observed since ancient times, and over the centuries, Mars has featured prominently in many cultures’ art and mythology. The Italian astronomer Galileo Galilei was the first to observe Mars through a telescope in the early 17th century. By the 19th century, advancements in telescope technology allowed astronomers to map its surface in greater detail.
Mars is also known as the “Red Planet” due to the prevalence of iron oxide on its surface, giving it a rusty, red appearance. It has two small moons, Phobos and Deimos, named after the horses that pulled the chariot of the Greek god of war, Ares. Interestingly, Phobos is gradually moving closer to Mars and is expected to either crash into the planet or break apart in about 50 million years.
Size and Distance of Mars
Mars has a radius of 3,390 kilometers, making it about half the size of Earth. If Earth were the size of a nickel, Mars would be about the size of a blueberry. It orbits the Sun at an average distance of 228 million kilometers (about 1.5 astronomical units), meaning it takes sunlight approximately 13 minutes to travel from the Sun to Mars.
Orbit and Rotation
Mars completes one rotation around its axis every 24.6 hours, very similar to an Earth day, which lasts 23.9 hours. A day on Mars is called a “sol,” short for “solar day.” A Martian year, or the time it takes Mars to complete one orbit around the Sun, lasts 669.6 sols, or about 687 Earth days.
Mars has an axial tilt of 25 degrees relative to its orbital plane around the Sun, close to Earth’s axial tilt of 23.4 degrees. This tilt gives Mars seasons similar to those on Earth, but they last longer because Mars takes more time to orbit the Sun due to its greater distance. The seasons on Mars are also uneven due to its elliptical orbit, with spring in the northern hemisphere (autumn in the southern hemisphere) being the longest season, lasting 194 sols, while autumn in the northern hemisphere (spring in the southern hemisphere) is the shortest at 142 sols.
Formation and Structure of Mars
Mars formed about 4.5 billion years ago as the solar system settled into its current layout. Like Earth, Venus, and Mercury, Mars is a rocky planet with a central core, a mantle, and a crust. Its core is thought to be composed of iron, nickel, and sulfur and has a radius of about 1,500 to 2,100 kilometers. Surrounding the core is a rocky mantle that is between 1,240 and 1,880 kilometers thick, and above that is a crust made up of iron, magnesium, aluminum, calcium, and potassium, ranging from 10 to 50 kilometers deep.
While Mars is often thought of as the Red Planet, it actually exhibits a range of colors on its surface, including browns, golds, and tans. The red color is due to the oxidation, or rusting, of iron in the rocks, soil, and dust that cover the surface. Despite its small size compared to Earth, Mars has a surface area nearly equivalent to all the dry land on Earth. It also hosts Olympus Mons, which is about three times taller than Mount Everest, and has a base the size of the state of New Mexico.
Mars’ Watery Past
Mars shows many signs of having had a watery past, with networks of ancient river valleys, deltas, and lake beds, as well as rocks and minerals that could only form in the presence of liquid water. Some evidence suggests that Mars experienced massive floods about 3.5 billion years ago. Today, water on Mars is mostly in the form of ice, particularly at the polar caps. Occasionally, salty liquid water can flow down some Martian hillsides and crater walls.
Atmosphere and Climate
Mars has a thin atmosphere composed mostly of carbon dioxide, nitrogen, and argon, with a hazy, red appearance due to the suspended dust. This thin atmosphere offers little protection from meteoroids, asteroids, and comets. Surface temperatures on Mars can range from 20 degrees Celsius to as low as -153 degrees Celsius. The thin atmosphere also means that heat from the Sun easily escapes back into space, resulting in cold temperatures. Mars often experiences strong winds that can stir up vast dust storms, covering much of the planet. After these storms, it can take months for the dust to settle back down.
Magnetic Field
Mars does not have a global magnetic field today, but its southern hemisphere crust is highly magnetized, indicating that it had a magnetic field about 4 billion years ago.
The Search for Life
Given what we know about Mars’ surface, atmosphere, and temperatures, scientists do not expect to find thriving life forms on its surface today. However, the search continues for signs of past life, particularly from a time when Mars was warmer and covered with water before it transformed into the arid planet we see today.
Mars Missions and Exploration
No planet has been studied as intensely as Mars, with observations dating back over 4,000 years to ancient Egyptian astronomers who tracked its movements across the sky. Today, NASA operates a fleet of robotic spacecraft studying Mars from every angle. On the surface, the Perseverance rover, the largest and most advanced rover NASA has sent to another world, landed on February 18, 2021. Two other NASA spacecraft are also active on the surface: the Curiosity rover, exploring Mount Sharp, and the InSight lander, studying the planet’s interior from its location on the flat plain of Elysium Planitia.
In the skies above, the Ingenuity helicopter, a part of the Perseverance mission, made history on April 19, 2021, when it became the first aircraft to make a powered, controlled flight on another planet. Meanwhile, three NASA spacecraft orbit Mars: Mars Reconnaissance Orbiter, Mars Odyssey, and MAVEN.
Other international missions have also reached Mars. The United Arab Emirates’ Hope orbiter arrived at Mars on February 9, 2021, and China’s Tianwen-1 mission, which includes an orbiter, lander, and rover, arrived on February 10, 2021. In May 2021, China’s Zhurong rover successfully landed, making China the second country after the United States to operate a rover on Mars. The European Space Agency has two missions in orbit, the ExoMars Trace Gas Orbiter and Mars Express. India’s Mars Orbiter Mission (MOM), which launched in 2013, continues to orbit Mars today.
