Mars, named for the Roman god of battle, has long been seen as a forerunner in the night sky. The planet’s rusty red surface, too, conveys a story of destruction in its own way. The fourth planet from the sun could have been mistaken for Earth’s smaller twin billions of years ago, with liquid water on its surface—and possibly even life.
The globe is now a frigid, desolate wasteland with scant evidence of liquid water. Scientists have revealed Mars as a dynamic, windblown planet that could, just maybe, host-microbial life beneath its rusty surface even today, after decades of research using orbiters, landers, and rovers.
Seasonal changes and a longer year
Mars is the seventh-largest planet in our solar system, with a radius of 2,106 miles and a diameter of nearly half that of Earth. It has a surface gravity of 37.5 percent that of the Earth.
NASA’s recent explorations of Mars have unearthed some of the planet’s greatest mysteries. This video describes how it differs from Earth and what would happen if humanity were to dwell there.
The duration of a Martian day, known as a sol (short for “solar day”), is defined by the rotation of Mars on its axis every 24.6 Earth hours. The axis of rotation of Mars is tilted 25.2 degrees relative to the plane of the planet’s orbit around the sun, allowing Mars to have seasons that are similar to those on Earth. Spring and summer are experienced by whichever hemisphere is slanted closer to the sun, whereas fall and winter are experienced by the hemisphere tilted away. Both hemispheres receive equal illumination at two precise times each year, known as the equinoxes.
Seasons on Mars, however, differ from those on Earth for a variety of reasons. For starters, with an average orbital distance of 142 million miles, Mars is nearly 50% further from the sun than Earth. This means that it takes Mars longer to complete a single orbit, lengthening its year and season lengths. A year on Mars is 669.6 sols, or 687 Earth days, and a season can be as long as 194 sols, or little over 199 Earth days.
The angle of rotation of Mars’ axis fluctuates much more frequently than that of Earth’s, causing temperature variations on timescales of thousands to millions of years. Furthermore, Mars’ orbit is less circular than Earth’s, resulting in greater variations in orbital velocity over the course of a Martian year. The timing of the solstices and equinoxes on Mars is affected by this annual change. The northern hemisphere’s spring and summer are longer than the southern hemisphere’s fall and winter.
Another complicating element is that Mars’ atmosphere is significantly thinner than Earth’s, limiting the amount of heat it can trap near its surface. Surface temperatures on Mars can range from 70 degrees Fahrenheit to -225 degrees Fahrenheit, but the average temperature is -81 degrees Fahrenheit, which is 138 degrees colder than Earth’s average.
Once upon a time, it was windy and wet!
The atmosphere of Mars, which is largely comprised of carbon dioxide, nitrogen, and argon, is the primary driver of present Martian geology. The air is ridiculously thin by Earth standards; the air pressure atop Mount Everest is nearly 50 times that of the Martian surface. Despite the thin atmosphere, Martian breezes may reach speeds of up to 60 miles per hour, kicking up dust that generates giant dust storms and strange sand dunes.
Wind and water did, however, formerly flow across the crimson planet. Robotic rovers have discovered evidence that lakes and rivers of liquid water flowed across the surface of Mars billions of years ago. This suggests that Mars’ atmosphere was sufficiently dense and maintained enough heat in the distant past for water to remain liquid on the red planet’s surface. Today, however, despite the abundance of water ice beneath the Martian surface and in its polar ice caps, there are no major lakes of liquid water on the surface.
Mars also lacks an active plate tectonic system, which drives our active Earth’s geologic engine, as well as a planetary magnetic field. The lack of this protective barrier makes it simpler for high-energy particles from the sun to peel away the red planet’s atmosphere, which could explain why Mars’ atmosphere is currently so thin. However, Mars appears to have had an inner dynamo powering a planet-wide magnetic field in the distant past, up to about 4.12 to 4.14 billion years ago. What caused the Martian dynamo to shut down? Scientists are still pondering the question.
High peaks and low troughs
Mountains, valleys, and volcanoes abound on Mars, like they do on Earth and Venus, but the red planet’s are by far the largest and most dramatic. The largest volcano in the solar system, Olympus Mons, stands 16 miles above the Martian surface, three times higher than Everest. However, because Olympus Mons’ base is so large—it spans 374 miles—the volcano’s average slope is only slightly steeper than a wheelchair ramp. The peak is so huge that it curls with Mars’ surface. Standing on the outskirts of Olympus Mons, the top would be visible beyond the horizon.
Not only does Mars have the highest highs, but it also has some of the lowest lows in the solar system. Valles Marineris, the red planet’s most famous canyon system, is located southeast of Olympus Mons. The gorges stretch for almost 2,500 miles and slash up to 4.3 miles through Mars’ surface. The chasm network is four times deeper—and five times longer—than Earth’s Grand Canyon, and it spans a stunning 200 miles at its widest point. Mariner 9, which landed at Mars in 1971 and became the first spacecraft to orbit another planet, gave the valleys their name.
Two hemispheres, two stories
Mars formed from the gaseous, dusty disc that enveloped our young sun about 4.5 billion years ago. The interior of Mars has evolved through time into a core, a mantle, and an exterior crust that is an average of 40 miles thick.
Its core, like Earth’s, is presumably formed of iron and nickel, although it contains more sulphur than ours. The best known estimations put the core’s diameter at 2,120 miles, plus or minus 370 miles—but we don’t know the exact dimensions. The InSight lander from NASA is attempting to decipher the secrets of Mars’ innards by measuring seismic waves as they travel through the planet.
The northern and southern hemispheres of Mars are diametrically opposed to one another, unlike any other planet in the solar system. The northern portion of the planet is primarily low-lying plains, with a crust as thin as 19 miles thick. The southern hemisphere’s highlands, on the other hand, are dotted with extinct volcanoes, and the crust there can be up to 62 miles thick.
What went wrong? It’s possible that internal magma flow patterns produced the change, but some experts believe it’s the result of one or more massive impacts on Mars. According to one new hypothesis, Mars gained its two faces when an asteroid the size of Earth’s moon collided with it near its south pole.
Both hemispheres have one thing in common: they’re covered in the planet’s signature dust, which is coloured by iron rust and comes in a variety of colours of orange, red, and brown.
Companions from the stars
Phobos and Deimos, the red planet’s two small, irregularly shaped moons, were acquired at some point in the distant past. The two lumpy worlds, discovered in 1877, are named after the Roman god Mars’ sons and chariot drivers. The origins of the moons are unknown. One theory is that they formed in the asteroid belt and were attracted to Mars by its gravity. Recent theories, on the other hand, propose that they may have formed from debris blasted up from Mars following a massive impact many years ago.
Deimos, the smaller of the two moons, circles Mars every 30 hours and has a diameter of less than 10 kilometres. Phobos, its larger twin, has several scars on its surface, including craters and deep grooves. The cause of the grooves on Phobos has long been a source of controversy among scientists. Are these the trails of rocks moving across the surface following an old collision, or are they indicators that Mars’ gravity is pushing the moon apart?
In any case, the moon’s future will be far less exciting. Each century, Phobos approaches Mars by roughly six feet; after 50 million years or so, the moon is expected to collide with the red planet’s surface or shatter into smithereens.
Mars missions are underway.
Humans have robotically investigated Mars more than any other planet beyond Earth since the 1960s. At the moment, eight missions from the United States, the European Union, Russia, and India are circling or roving around Mars’ surface. However, reaching Mars safely is no easy task. Since 1960, 26 of the 45 Mars missions have had a component fail to leave Earth, become silent en route, miss orbit around Mars, burn up in the atmosphere, crash on the surface, or die prematurely.
More missions are on the way, including some that will aid in the quest for life on Mars. NASA is preparing the Mars 2020 rover to store promising samples of Martian rock that will be returned to Earth by a future expedition. The European Space Agency and Roscosmos plan to launch a rover named after chemist Rosalind Franklin in 2020. Her work was essential in determining the structure of DNA. The rover will burrow into Martian soil in search of past and contemporary signs of life. Other nations are joining the fray, bringing space exploration closer to a global scale. The United Arab Emirates plans to launch its Hope orbiter to research the Martian environment in July 2020.
Perhaps humans will eventually join robots on Mars. NASA has indicated that returning people to the moon will serve as a stepping stone to Mars. Elon Musk, the founder and CEO of SpaceX, is developing the Starship, a gigantic vehicle that will be used to take humans to Mars. Will humanity establish a scientific base on Mars’ surface, similar to those found in Antarctica? What impact will human activity have on the red planet and our efforts to find life there?
We’ll have to wait and see. Mars, though, will continue to capture the human imagination as a gleaming red beacon in our skies and stories, no matter what happens.