1 {photo of Mars}
1 Caption: The Red Planet

Mars as seen through a small telescope. Creative Commons Attribution-ShareAlike image by Jeff Barton.

The colour red has long been associated with anger, rage, and war. It attracts the attention like no other colour, and it is the colour of freshly spilt blood. So when the Ancient Romans looked into the night sky and decided that the wandering stars they could see moving slowly amongst the fixed canopy of the heavens were gods, it was patently clear which of these planets belonged to the god of war. And so the red planet received the name of Mars.

Even in the city where you can see a scant handful of stars, if you look in the right place at the right time it is easy to pick out Mars. It is fairly bright and has an obvious red hue. The only things you're likely to confuse it with are the three giant red stars Aldebaran (the eye of Taurus, the bull), Antares (the heart of Scorpius^[1]), and Betelgeuse (at Orion's shoulder). But stars twinkle (or scintillate) as their light passes through the turbulent atmosphere above us, while Mars glares down balefully with a steady red glow. The other planets are white dots, so it's clear that Mars is something special.

Indeed, no other planet has fascinated us so much. The prototypical alien is the Martian, a term almost synonymous with "extraterrestrial" for decades around the middle of the 20th century.

Up until the invention of the telescope, Mars was simply a cryptic red light in the sky. As one of the planets, its motions were studied and catalogued. The path of Mars through the background of stars was complicated and intriguing. Normally it moved westward. But occasionally it would slow, halt, and reverse directions, as if unable to make up its mind. This motion was dubbed retrograde (a fancy word for "reverse"), and it became portentous. If the god of war was doing something unusual, surely that indicated troubled times on Earth.

Giovanni Schiaparelli. Public domain image from Wikimedia Commons.

The Greek astronomer Ptolemy had explained the motions of Mars relative to a fixed Earth at the centre of the universe. According to his vision of the universe, everything in the heavens was perfect. Naturally then, the stars and planets moved in perfect circles, at constant speeds. The fact that the planets did not move uniformly across the sky led Ptolemy to propose that the planets actually moved around a smaller circle, and the centre of this circle moved uniformly around the Earth along a larger circle. This gave the planets a looping motion that resembled their back and forth motions relative to the stars. The small circle that produced this motion was called an epicycle. Ptolemy's model of the universe stood essentially unchallenged for 14 centuries.

In the mid 16th century, the Polish astronomer Nicolaus Copernicus realised there was a simpler explanation for the retrograde motions of the planets. If you placed the sun at the centre of the universe and made the Earth and the planets circle around it, then this neatly explained both why Mercury and Venus never ventured far from the sun, and the retrograde behaviour of the other planets. From the point of view of someone standing on Earth, Mars would appear to be going backwards when Earth was overtaking it on the inside lane, so to speak, even though it was in reality moving steadily all the time.

There was some controversy over this demotion of Earth from the centre of the universe, which I won't go into further today. But Copernicus's view prevailed and the job of the next generations of astronomers was to measure the positions of the planets more precisely so that their orbits could be described accurately. Danish astronomer Tycho Brahe made probably the most accurate measurements before the invention of the telescope, and the German Johannes Kepler inherited them. It was clear by this point that Mars defied the system. Its position in the sky did not seem to fit with it moving in a circle centred on the sun. Kepler resolved to solve the problem of fitting the planet to Tycho's observations, and declared he would tame Mars within a week. In the end, it took him several years.

Surface of Mars, as drawn by Schiaparelli. Public domain image from Wikimedia Commons.

Kepler's first stroke of inspiration was to move the circle of Mars's orbit so that the sun was offset a little from the centre. This made its motions better fit the observations. Next Kepler allowed its speed to vary, so that Mars moved faster when it was nearer the sun and slower when further away. A better fit again. Finally, Kepler realised that if the circle was squashed into an ellipse, the motion of Mars would be exactly as observed. The fact that the planets moved in elliptical orbits, changing speed as they moved around the sun, turned out to be exactly what you would get if the sun attracted the planets with a force that fell off as the square of the distance, as Isaac Newton later calculated. And so the red planet played a pivotal role in our understanding of gravity.

When the telescope was invented, Mars was naturally one of the first objects observed. And this too led to astonishing discoveries. Mars had features on its surface. It was red, but it had dark patches. And it had white patches at the north and south poles, which grew and shrunk in size as the seasons changed. Rather than being a point of light in the sky, it became clear that Mars was a world.

When the Italian astronomer Giovanni Schiaparelli observed Mars, he noted down some of the surface features and gave them names. He thought he saw vaguely line-like features, and called them canali, the Italian word for channels, such as made by rivers. When Schiaparelli's observations became known to English-speaking astronomers, they misinterpreted the word as canals. This fired the imaginations, none moreso than the American Percival Lowell.

Percival Lowell. Public domain image from Wikimedia Commons.

Lowell was a wealthy businessman and diplomat, who maintained a keen interest in astronomy throughout his life. When at the age of 38 he saw Schiaparelli's notes on Mars, he decided to build a state of the art observatory, funding it entirely from his own pocket, and dedicate himself to being its chief observer. The Lowell Observatory in Flagstaff, Arizona, began observations in 1896, and Lowell dedicated the remaining 20 years of his life to astronomy. Much of that time he spent observing Mars, drawing maps of the canals he thought he could discern through the telescope, and writing speculative articles and books about who could possibly have built them.

This may all sound rather deluded now, but at the time the idea of life and a civilisation of some sort on Mars was seriously considered among scientists. The books Lowell wrote gave it respectability. This crossed over into fiction, with Edgar Rice Burroughs developing his popular Barsoom series beginning in 1911, directly from the best available scientific theories of Mars at the time, if embellished with Victorian era ideas of romantic fantasy adventure. And although better observations would later reveal that much of what Lowell thought he saw through his telescope on the surface of Mars was more the product of his own fervent hope than reality, several of the features that Schiaparelli had drawn do line up with features on our present maps of Mars, and have inherited the names he gave them. The most striking features that Schiaparelli clearly got right are the large southern hemisphere impact basins of Hellas and Argyre.

At the same time that Lowell was obsessed with observing Mars, and Burroughs with imagining what life and adventure would be like on Mars, American physicist and engineer Robert Goddard was obsessed with getting to Mars. He was born a few years too early to grow up on Burroughs' fantasies, but at the right time to read H. G. Wells' 1898 novel The War of the Worlds when 16 years old. A year later he had the chore of trimming dead branches off a cherry tree on his father's farm. Later he wrote about that day:

Martian canals as drawn by Percival Lowell. Public domain image from Wikimedia Commons.

On this day I climbed a tall cherry tree at the back of the barn... and as I looked toward the fields at the east, I imagined how wonderful it would be to make some device which had even the possibility of ascending to Mars, and how it would look on a small scale, if sent up from the meadow at my feet.

Goddard's life was transformed that day, and he dedicated the rest of his life to researching the question of what it would take to propel an object off the Earth's surface into space, and how a device to achieve this could be built. Goddard was smart and practical, but he was also a visionary. Outspoken about his ideas for sending objects into space, at first he was ridiculed. But his calculations and then practical experimental work on rocketry, building on the purely theoretical foundations of the Russian physicist Konstantin Tsiolkovsky, showed that rockets could be made practical devices. Goddard played a vital role in the development of rocketry which ultimately led to artificial satellites, sending humans into space, the Apollo programme, and the robotic probes we now send to explore the solar system.

Valles Marineris, mapped by NASA's Mars Odyssey. If you want to blow your mind, download the higher-res version (9MB) or highest-res version (WARNING: 84MB). Public domain image from Wikimedia Commons.

Naturally, a prime target for those probes has been and continues to be Mars. The first probe to Mars was Mariner 4 in 1965. The photos it returned from nearby space as it flew by represented the first time anyone had seen Mars from closer than the surface of the Earth. We really had no idea what to expect. It could have been civilisations, or forests and animals. What Mariner 4, and its two followers Mariner 6 and 7, found was a crater-pocked landscape that resembled our lifeless moon and an atmospheric pressure barely 1% of that on Earth.

In 1971, Mariner 9 became the first probe to enter Mars orbit, from where it beamed back 7329 images of the surface over almost a year of operation. This filled in over 80% of our map of Mars, giving us our first complete map of the planet. It turned out the previous probes had seen relatively boring parts of the surface, because Mariner 9 discovered staggering geological features they had missed. Olympus Mons, the largest volcano we know of anywhere, the great chain of lesser but still enormous volcanoes in the enormous plateau of Tharsis, and the mind-boggling canyon named in honour of Mariner 9 itself: Valles Marineris. Valles Marineris shows branching side canyons that look unmistakably like river canyons.

It seems clear that Mars once had flowing water, but now the planet is too cold and the only water remaining on the surface is frozen into the ice caps seen at the poles. The thin atmosphere means there is little protection from dangerous cosmic rays. Any Martians, scientists argued, would perhaps be microbes at best, or non-existent at worst. To settle this question, the Viking mission in 1976 comprised two orbiters and two surface landers equipped with chemical labs to analyse the Martian surface for evidence of biological activity. Its results were... ambiguous. The chemistry of the Martian soil is different to what we are used to on Earth, so it was difficult to interpret the results and the experiments were not conclusive.

Mars, showing size of Valles Marineris, mapped by NASA's Viking 1. The three dark dots on the left are the Tharsis volcanoes. Public domain image from Wikimedia Commons.

The latest Mars lander, the rover Curiosity, is equipped with far more sophisticated analysis tools, designed to look for evidence of wet conditions that could have supported life in the past, as well as take inventories of organic compounds and look for fossil features which may be biological in origin. It is not equipped to look directly for living organisms.

Mars still fascinates us. We may have lost the canals and the Martians^[2], but we have gained something far greater - knowledge and the awe of nature. One day, perhaps within our lifetimes, humans will travel to Mars and walk on the surface of another planet. We have visited our moon, but that is like putting your toes in the water on the scale of the universe. By getting to Mars, we will be wading in up to our knees. We will be exploring the tide pools and the things that scurry under rocks as the waves of the cosmic ocean lap gently around our ankles. We—or perhaps our robots may beat us to it—may find the first compelling evidence that we are not alone in the immensity of space. There is a lot to learn, about both the universe and ourselves.

Mars, the god of war, may be our greatest step yet to harmony and enlightenment. It has already inspired many individuals throughout history to achieve things far beyond what they would have imagined when they first saw the red planet. But the most exciting time in the human understanding of Mars is just around the corner in front of us.

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Title image: Public domain image by NASA, from Wikimedia Commons.

[1] The constellation name is Scorpius, though most people probably think of it as Scorpio, following the astrological nomenclature.

[2] Although not entirely. The growing steampunk aesthetic lends itself to Victorian imaginings, including the notion of a Mars inhabited by a canal-building civilisation. The roleplaying game Space: 1889 explores the possibilities and provides a popular setting for gaming adventure in such a world.