Slow Orbit · Episode 3 · 16 min

Mars

The red planet, slowly: its rusted dust and blue sunsets, the greatest volcano and canyon in the Solar System, the old riverbeds, two small moons, and the patient machines that still work there. Read by a synthetic voice. Script written and fact-checked by the show's team.

The script

Slow Orbit. Lecture three... Mars.

This lecture is read by a synthetic voice.

In the night sky, there is one light that is not quite like the others.

It does not twinkle very much. It moves slowly against the stars, from one month to the next. And it has a colour... a faint, warm, orange-red, like the last glow of an ember.

People have watched it for as long as there have been people watching the sky. Because of its colour, many of them thought of blood, and of war. The Romans gave it the name of their god of war... Mars. The name has stayed.

Mars is the fourth planet from the Sun.

It travels around the Sun at an average distance of about two hundred and twenty-eight million kilometres... about one and a half times as far as the Earth. So the Sun, seen from Mars, looks a little smaller, and its light is a little weaker... less than half as strong as the light that falls on the Earth.

One journey around the Sun takes Mars six hundred and eighty-seven Earth days... almost two of our years.

But its day is very nearly our own. Mars turns once on its axis in twenty-four hours and thirty-seven minutes. The days and nights on Mars come at almost the same pace as they do here.

And because the planet is tilted, much as the Earth is, Mars has seasons. Spring, summer, autumn and winter... each of them nearly twice as long as ours.

Mars is a small world.

Across its middle, it is about six thousand seven hundred and eighty kilometres... a little more than half as wide as the Earth.

Its pull is weak. On Mars, everything weighs a little more than a third of what it weighs at home. A stone dropped from the hand falls slowly, and lands softly, in the dust.

The air of Mars is very thin.

It is made almost entirely of carbon dioxide, and it presses down on the ground with less than one hundredth of the weight of the air on Earth. Water cannot stay as a liquid on the surface for long... in that thin air, ice turns straight to vapour, and drifts away.

And it is cold. On an ordinary day, the average temperature across the planet is far below freezing... around sixty degrees below zero. At midday, near the equator, in summer, the ground can warm above freezing... sometimes to around twenty degrees. At night, it falls again, quickly, toward minus eighty, minus one hundred.

Everything on Mars is the colour of rust.

And that is exactly what it is. The dust and the rocks are rich in iron, and over billions of years, the iron has slowly rusted. A fine, red-brown dust lies over almost everything... over the plains, over the stones, in the hollows of the craters.

The wind lifts the dust, and carries it. On a calm day, it hangs in the air as a pale haze, and the sky above Mars is not blue, but a soft butterscotch, the colour of weak tea.

And then, at the end of the day, something strange happens.

As the Sun goes down, the sky around it turns blue. A cold, pale blue, glowing around the setting Sun, while the rest of the sky stays warm and dusty. The fine dust in the air scatters the light in its own way... and on Mars, the sunsets are blue.

Sometimes, the wind rises.

In the spring and summer of the southern half of the planet, dust storms begin. Most of them are small, and pass in a few days. But every few years, the storms join together, and grow... until a veil of dust covers the whole planet, and hangs there for weeks, or months.

From the Earth, through a telescope, the markings on Mars fade, and disappear. On the ground below, the light grows dim, the sky turns dark orange, and the Sun becomes a pale disc behind the dust.

And then, slowly, the dust settles, and the planet appears again.

Mars has mountains greater than any on Earth.

The greatest of them is a volcano called Olympus Mons. It rises about twenty-two kilometres above the average level of the planet's surface... more than twice the height of Everest. Its base is about six hundred kilometres across. Its slopes are so wide and so gentle that someone standing on them, in the middle, would never see the summit at all... only a long, slow rise of ground, going up into the sky, past the horizon.

It is quiet now. It may have been quiet for a very long time.

And Mars has a canyon greater than any on Earth.

It is called Valles Marineris... the valleys of the Mariner, after the spacecraft that first photographed it. It runs along the middle of the planet for more than four thousand kilometres... as far as from one side of a continent to the other. In places, it is seven kilometres deep.

On Earth, a canyon like this would be carved by a river. This one was not. It is a great crack in the surface of the planet, pulled apart long ago, and widened over time by landslides, and wind.

At the top and the bottom of the world, there are caps of white.

At each pole of Mars, a cap of ice lies over the ground... mostly frozen water, layered with dust, with a thin coat of frozen carbon dioxide on top in winter.

As the seasons turn, the caps grow, and shrink. In the long Martian winter, the air at the poles grows so cold that part of the atmosphere itself freezes, and falls as frost.

Seen from far away, the white caps come and go with the seasons, as they have for a very long time.

Mars is a dry world now.

But it was not always dry.

Across its surface, there are long, winding valleys, cut by flowing water. There are the dry beds of old lakes, and the fan-shaped deltas where rivers once ran into them. There are rocks that could only have formed in water, and smooth, rounded pebbles, polished by streams long ago.

Billions of years ago, Mars was warmer, and wetter. Its air was thicker. Water ran across its surface, and gathered in lakes, and perhaps, in places, in seas.

Over a very long time, the air thinned, and the water was lost... some of it into space, some of it frozen into the ground, where much of it still lies today.

Whether anything ever lived in those old lakes is one of the great open questions. No one knows yet.

Two small moons circle Mars.

They were found in 1877, by an American astronomer named Asaph Hall, who gave them the names of the two sons of the god of war... Phobos, and Deimos. Fear, and Dread.

They are not round. They are small, dark, lumpy worlds, more like potatoes than moons. Phobos is about twenty-two kilometres across. Deimos is smaller still... about twelve.

Phobos travels very close to the planet, and very fast. It circles Mars three times in a single Martian day, rising in the west and setting in the east.

And it is slowly falling. Little by little, Phobos is moving closer to Mars. In some tens of millions of years, it will come too close... and it will either break apart into a ring around the planet, or fall.

But that is a long time away.

For a long time, people could only look at Mars from far away.

Then, in the second half of the twentieth century, the first spacecraft flew past it, and sent back pictures of craters, and dust, and dry valleys.

In 1976, two landers named Viking settled onto the surface, and looked out over the plains. For the first time, people saw the ground of Mars from Mars itself... a field of rocks, under a pale, dusty sky.

Since then, many machines have followed.

Small wheeled rovers, driving slowly across the dust, with cameras for eyes. One of them, named Opportunity, was built to work for about ninety days. It kept working for almost fifteen years, until a great dust storm covered the Sun, and its batteries could no longer be charged.

Others are still at work. A rover called Curiosity has been climbing the slopes of a mountain in the middle of a crater since 2012, reading the layers of rock one by one, like the pages of a book.

And in 2021, another rover, Perseverance, landed in an old crater that once held a lake. It brought with it a tiny helicopter, Ingenuity... and on an April morning, in the thin air of Mars, the helicopter lifted from the ground, and flew. The first powered flight on another world.

Every message to and from these machines crosses the gap between the two planets at the speed of light.

When the planets are close, a message takes about three minutes to arrive. When they are far apart, on opposite sides of the Sun, it takes more than twenty.

So no one on Earth can drive a rover by hand. Each day, the people who look after them send their instructions... and then wait, while the rover carries them out, alone, and sends back its pictures of the day.

Somewhere on Mars, right now, it is evening.

The light is going down over a wide plain of red-brown dust. The Sun is small, and low, and around it, the sky is turning blue.

A thin wind moves over the ground, lifting a little dust, and setting it down again. The temperature is falling. Overhead, the first stars are coming out... and among them, if one knows where to look, there is a small, bright, blue-white point of light.

It is the Earth.

From here, it is only a star among stars... a little brighter than the rest. It rises in the morning, or shines in the evening, and then it sets, and the long, cold night of Mars comes down over the plains.

And from the Earth, on clear nights, Mars still rises over the horizon... that same faint, warm, orange light, moving slowly against the stars, the way it always has.

Slow Orbit.

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