Read | Our view of Mars — past, present, and future
by Paul Cornish
Header image credit: Stellarium/ NASA
From your window
Families and Adults
Have you ever noticed a bright point of orangey-red light shining in the night-sky? Chances are you’ve spotted Mars — a planet that’s captivated humankind for thousands of years.
Throughout time that orangey-red light has meant different things to different people. Long ago we were curious about its colour and the way it moved across the sky. Eventually we began to ask ourselves what — or who — could be living on this distant world.
These days we’re wondering, can we get people on the surface of Mars? The more we learn about the red planet the bigger the questions seem to get.
Thousands of years ago…
The Romans gave it the name we still use in English today. To the Romans, Mars was the guardian of agriculture as well as a god of war. He could either be a farmer's best friend, or a savage warrior. Perhaps this is why he was associated with a planet whose appearance in the sky changes dramatically from year to year?
Sometimes Mars appears small and faint, while other times it's fiercly bright. This is all down to its distance from Earth.
Earth is closer to the Sun than Mars — it has a smaller orbit, and so moves faster. Earth takes 365 days to complete one orbit of the Sun. In other words, it takes a year to go around the Sun once. Mars on the other hand, takes almost two years — around 687 days. As a result, Mars’ brightness in the sky changes from year to year.
For example, in May 2019 Earth was far away from Mars and so Mars appeared faint in our sky. But by May 2020 Earth had began to catch up with Mars, and so Mars appeared a lot brighter to us. By October 2020 Earth was between Mars and the Sun and the red planet appeared even brighter!
The fact that Earth moves around the Sun faster than Mars also means that Mars doesn’t appear to move in a straight line. It seems to make little loops as it moves across our sky.
As Earth overtakes Mars we go from looking ahead at Mars, to looking behind. As a result, Mars seems to move backwards in our sky. As Earth moves even further ahead Mars will once again appear to move in its regular direction.
This is called retrograde motion, and it fascinated ancient astronomers. In fact, it’s possible that the oldest star map ever known shows Mars in retrograde. The map is around 3500 years old and was found on the ceiling of the tomb of Senenmut, an Egyptian architect.
In this map Mercury, Venus, Jupiter, and Saturn are represented by four people in boats, but there doesn’t seem to be any obvious sign of Mars. Some historians say that Mars is represented on the map by an empty boat that’s separate from the others — possibly because it was moving backwards at the time the map was made.
A part of the map in Senemut’s tomb.
Credit: SenemmTSR/ Public Domain
Hundreds of years ago…
Many years later astronomers began to observe Mars with telescopes, with Galileo Galilei being the first person to do so in 1610. By the 19th century telescopes were powerful enough to make out details of the surface of Mars, and this led to some interesting “discoveries”.
In 1877, an Italian astronomer named Giovanni Schiaparelli produced the first detailed map of Mars. These maps contained features he called canali — long, straight lines that he named after famous rivers on Earth.
1877 map of Mars by Giovanni Schiaparelli.
Credit: Unknown author / Public domain
Canali, which means “channels” or “grooves”, was often mistranslated in English as “canals”. In 1894 a few astronomers, most famously the American astronomer Percival Lowell, began to discuss the idea that the canali were really canals made by intelligent aliens.
Lowell studied the canali for years. He thought that Mars was once covered in lush vegetation, but all the water had dried up, forcing the Martians to build canals to spread water from the poles around Mars
Lowell’s theories were popular with the public, receiving coverage in newspapers and magazines.
Lowell wrote three popular books on Mars, and even founded an observatory with a custom-made telescope that he used to study Mars. The observatory was built on a mountain peak in Arizona that Lowell named Mars Hill.
An article about Lowell from Answers Magazine, 1906.
Despite Lowell’s popularity with the public, other astronomers weren’t so sure of Lowell’s claims. In 1907 Alfred Russel Wallace, who is most famous for his work on the theory of natural selection with Charles Darwin, wrote that canals would actually be a really wasteful way of transporting water across a desert planet, as so much of the water would evaporate. He said that if aliens had indeed built canals then it would show "complete ignorance and stupidity in these alleged very superior beings."
Lowell may not have actually been seeing anything on the surface of Mars. He would stop down his telescope — mask part of it to create a smaller hole — in an attempt to improve the view. It’s possible that in doing so Lowell accidentally turned his telescope into an ophthalmoscope — an instrument for studying the eye. This means that rather than studying canals, Lowell may have been studying an image of the shadows of blood vessels cast on the retina of his own eye.
Lowell was wrong about canals and Martians, but he still made an important contribution to science, and the world. His ideas inspired many science fiction authors, including H.G. Wells’ 'The War of the Worlds'. This story of Martian invaders who are jealous of our water was first published in 1897 and is still being told on TV and in cinemas today.
The observatory that Lowell built in Arizona today receives thousands of visitors every year. Discoveries made at the Lowell Observatory include the dwarf planet Pluto and many astronauts received training there as part of the Apollo Program. Not bad for a man who may have accidentally based his whole career around the inside of his eyes.
These days we can look at Mars in a lot more detail. We know that Mars is red because of iron oxide — a rusty dust that covers the whole surface. We know that there’s no canals, no flowing water, and sadly no life. There is however lots of water ice on Mars, with much of it at the North and South poles of the planet.
While most of the planet is cold, dusty, and dry today, scientists believe that billions of years ago it was a much wetter place. Mars is full of canyons, valleys, and mountains that scientists believe — based on what they know of Earth — were carved out by lots of flowing water a long time ago.
How Mars may have looked billions of years ago.
These oceans didn’t last. Mars has no magnetic field, which meant that there was nothing to stop its atmosphere from being stripped away over time by charged particles from the Sun. Eventually Mars’ atmosphere was so thin there wasn’t enough pressure to keep the flowing water on the ground. Some of it froze, but most of it drifted off into space.
Scientists don’t think that the water was around long enough for life to develop on Mars. If life did develop, it would have been simple, single celled life — microorganisms.
We know much more about Mars than we did in Lowell’s day, and it’s not just because of more powerful telescopes. Since 1960 scientists have been exploring Mars with space probes.
Mariner 9 discovered a volcano that came to be known as Olympus Mons that’s over twice the size of Mount Everest. It also discovered a huge 4000 km long system of canyons that was named Valles Marineris, after the probe.
Lots of probes have been sent to Mars since then. Some of them orbit the planet like Mariner 9, while other probes land on the surface - not always successfully. In 2003 the British probe Beagle 2 failed to open two of its four solar panels, meaning that it could never send any information back to Earth.
Mars has become a planet inhabited entirely by robots. Some of them are even capable of moving across the surface. These are the rovers!
NASA has sent five rovers to Mars in total. They’re sort of like remote-controlled cars that can be controlled by scientists on Earth. They explore Mars and send information back to Earth.
Sojourner became the first rover to explore Mars in 1997. It was about the size of a microwave oven. Sojourner sent photographs of the surface of Mars back to Earth and studied the rocks and dust, as well as the wind on Mars. It lasted 85 days before NASA lost contact with it.
A photo taken by Sojourner of its lander, including the airbags that cushioned the impact during landing.
Sojourner was followed in 2003 by the twin rovers Spirit and Opportunity — each the size of a golf cart. The twins were sent to opposite sides of the planet to find more clues about the history of water on Mars, and to see if the planet could ever have supported life.
Spirit sent back the first colour photos taken by a rover on another planet and found several signs of past water, exploring sites that may have been hot springs millions of years ago.
Opportunity also sent back photos and found evidence that its landing site was once the shoreline of a salty ocean.
Both rovers showed scientists that long ago, water on Mars may have looked a lot like water on Earth. NASA lost contact with Spirit in 2010. Opportunity kept sending information to Earth until 2018, when its solar panels got covered in dust and it finally stopped working.
A false colour, cropped version of the last panorama taken by Opportunity.
Curiosity landed on Mars in 2012. It’s about the size of a car and has been investigating if Mars once had the chemical ingredients for life.
One of the ways Curiosity does this is by drilling holes into what was once the bed of a Martian lake. It then searches the powder drilled from the rock for signs that these chemical ingredients were once there.
In 2018 Curiosity found organic molecules in the 3-billion-year-old rock. It’s not definite proof that there was once life on Mars but it’s a step in the right direction.
A 2-inch deep hole drilled by Curiosity.
Curiosity is still operational, and its mission has been extended indefinitely.
In February 2021 Perseverance, a rover about the same size as Curiosity, landed on Mars. Perseverence has been sent by NASA to look for signs of past and present life, and investigate if humans could one day explore Mars.
An image of Martian cliffs taken by Perseverance.
Perseverance has a companion. Ingenuity is a robotic helicopter that travelled to Mars attached to the underside of Perseverance. Its purpose was to test powered flight in the thin Martian air. It’s been very successful and has made several flights. It’s even sent back images taken while flying on Mars.
Thanks to Ingenuity, more robotic helicopters could be sent to Mars in the future. They’ll allow us to peer into areas that are too steep or slippery to send a rover.
The backshell and parachute of Perseverence, photographed from above by Ingenuity.
There’s one more rover on Mars, but it doesn't belong to NASA. On the 14th May 2021, Zhurong became China’s first rover to land on another planet. It has continued to study the rocks and weather of Mars long past its original 90 day mission.
A selfie taken by Zhurong on Mars, with it's lander.
Credit: China News Service.
Our view of Mars in the future…
Organisations from all over the world have been planning to send humans to Mars since the 1950s. This would be no easy task!
Astronauts could potentially be facing 9 months in a rocket just to get there, followed by 500 days on the surface waiting for Mars to be in the ideal position for them to return to Earth, and then a journey of 9 months home.
During those 500 days on the surface they would be faced with the challenge of surviving on a dry, dusty, lifeless world, with a thin atmosphere made mostly of carbon dioxide and no liquid water on the surface.
Whatever happens it can’t possibly be long before somebody sets foot on the dusty Martian surface for the first time.
Personally, studying the history of our relationship with the Red Planet fills me with hope. Humans are driven by our incredible curiosity. We’ve gone from wondering why Mars appears to move backwards in the sky, to imagining what the surface of this alien world may be like, to sending robots across space to answer our questions for us.
In a few years we may well be able to look at that orangey-red light in the night-sky and know that there is another human on it looking back at us.
If you’d like to find out a bit more about the red planet then take a look at the video below. It was originally live streamed on Facebook, and I use the free Planetarium software, Stellarium (download it here!) to look for Mars.