We're Going Multiplanetary

We're Going Multiplanetary

Stephen Hawking once said that humanity must colonise other planets in the 21st century if we want to avoid extinction.

Why Be a Spacefaring Civilisation?

Stephen Hawking's fears for humanity took the form of pandemics, nuclear war, asteroid impacts, and climate change. In order to avoid another Dark Age—or altogether extinction of the human species—we need to become a multiplanetary civilisation.

"You want to wake up in the morning and think the future is going to be great—and that's what being a spacefaring civilization is all about." - Elon Musk on SpaceX
Illustration of the SpaceX Starship on the moon looking back at Earth

The SpaceX Starship on the moon.

Are We Ditching Earth Now?

Perhaps the biggest criticism of becoming a multiplanetary civilisation is that we're giving up on Earth, having mined it for its natural resources and primed the climate for ruin. It's true: our industrial revolution has taken a huge toll on Earth's environment and biodiversity. We've witnessed wide-scale extinctions at our own hands. We should, as a civilisation, take the responsibility to fix that.

But consider our fate in 50,000 years' time, when the next glacial period will ravish the land, creating catastrophic cooling, range contractions, and extinctions. It will last for 90,000 years. Humanity itself may not survive—yet the third rock from the sun will still be here doing its thing long after we're gone.

Earth will die in 7.5 billion years when it's absorbed by the sun

Earth will be around for another 7.5 billion years before being absorbed by the sun.

Humans are a blip on the geological timeline. As a civilisation capable of self-preservation, we must hedge our bets by forming independent colonies on other moons and planets. We'll distribute the eggs of humanity across multiple baskets, so that one catastrophic basket loss won't commit our species to extinction.

If the dinosaurs had possessed this capacity, they'd have gone multiplanetary too. It's a matter of survival.

Terraforming Other Planets

Life on Earth evolved over billions of years under Earth's unique environmental conditions. Mammals speciated over 178 million years, with only the fittest adapting to the changing climate and ecological niches. Modern humans are the latest result of this environmental priming, and we thrive under the current conditions on Earth.

Any alien world we plan to inhabit must offer similar conditions. At the very least, we must be able to recreate them with supplies drawn mostly locally. We don't want to go to Mars only to have to live permanently in pressurised buildings. While it may start out that way, the long term goal is to tailor the atmosphere, biosphere, and climate to our biological needs.

Our effectiveness will not only determine the quality of life of Martian colonists, but their future evolution too.

Back in the 1960s, Star Trek referred to terraforming—literally "Earth-shaping"—other worlds by modifying the atmosphere, ecology, and surface topography to make them habitable to humans. Today, this fiction is becoming a necessary reality.

Illustration of Mars being terraformed into an Earth-like planet

Mars could be terraformed into an Earth-like planet with oceans and a milder climate.

Getting to Mars

To date, 40 attempts to send exploration vessels to Mars have resulted in 18 successful missions. The rest crash landed, broke down soon after arrival, or simply disappeared without a trace. But that's par for the course: this is space exploration we're talking about. There are a lot of unknowns.

Through SpaceX, Elon Musk has set his sights on a manned mission to Mars in 2024. The mission will check on water resources and local hazards, then establish mining, power, and life-support infrastructure. Colonisation can occur rapidly thereafter.

Illustration of the first city on Mars

The first city on Mars will be a self-sustaining network of industrial and residential buildings

The moment we leave the protective shroud of the Earth's atmosphere and magnetic field, conditions in space become pretty inhospitable. Our spacecraft must be designed and equipped to overcome challenges as wide-ranging as baseball-sized space debris ripping through the hull, to safely disposing of astronaut poo.

The journey to Mars lasts about six months. This varies, however, because the distance between Earth and Mars changes due to their independent orbits. Mars last made a close approach to Earth in October 2020, bringing them 62 million km (39 million miles) apart. On average, though, the straight line distance is more like 225 million km (130 million miles).

The transfer orbit between Earth and Mars in space

The transfer orbit between Earth and Mars requires a minimum six-month trek.

A realistic spacecraft trajectory from Earth to Mars has to take into account the continual movement of Mars, as well as avoid passing too close to the sun. Fortunately, rocket scientists love working this stuff out, and we can aim for these optimal launch dates every couple of years.

En route, astronauts need to deal with any and all issues that arise, without relying on real-time conversation with support crews on Earth. That's because communications are delayed by 3-22 minutes.

There's are also difficulties posed by the physical and psychological isolation of space travel that helps drive the plot of every single space movie ever. Not everyone is suited to being stuck in a cramped space vessel for six month, and colonists will need to meet minimum standards of mental and physical health.

Alien taught us that in space, no-one can hear you scream. Although in a confined spacecraft, your crew mates may beg to differ, politely requesting you keep your psychosis to yourself.

Colonising Mars

So, we've made it to Mars. What's it like living on this alien planet?

In one sense, it's very boring. This was borne out by volunteers who spent a long stint in a fake Martian habitat on a mountain in Hawaii. Check out The Habitat podcast for how it went. Time dragged, cabin fever set in, relationships got complicated, and people back home died. Still, they held out to the end, showing remarkable resilience when they could have chosen to walk away at any time.

Illustration of an astronaut on Mars before colonisation

Astronauts on Mars face extreme isolation before the first colonies arrive.

But boredom is the least of our concerns. Logistically, there are far more daunting physiological effects to tackle thanks to the vastly different environment conditions on Mars.

The orangery-brownish planet is about half the size of Earth, with just 10% of the mass. This creates a gravity problem. If you weigh 80kg (175lbs) on Earth, then you'll weigh 30kg (60lbs) on Mars.

Moving around in 38% the gravity may sound like awesome fun, but it has substantial downsides. Your body is adapted to Earth's gravity, so on Mars your bones and muscles will quickly degrade. What's more, you just spent six months in the zero gravity of the spacecraft. By comparison Mars would actually make you feel heavy.

In the zero gravity of space, astronauts lose bone density at a rate of 1% per month. Scott Kelly spent 340 straight days in space aboard the ISS, performing 2.5 hours of exercise every day to maintain bone and muscle strength. If you ever want to return to Earth, you'll need to keep strong or face major rehabilitation.

Illustration of SpaceX Starship taking off on Mars

The SpaceX Starship will ferry people to and from Mars.

Mars takes almost twice as long as Earth to orbit the sun, with a year lasting 687 days. But its the day-night length that poses problems. The 24 hours and 38 minutes of each Martian day will cumulatively impact on your circadian rhythms, triggering sleep disruption, mood changes, and insomnia.

Both Mars and Earth have similar axial tilts which give rise to seasons on both planets. But unlike Earth, Mars is made chiefly of iron-rich rock, producing the dust that gives it the nickname of the Red Planet. Vast dust storms—the largest observed in our solar system—can rage for months, sometimes covering the whole planet in a thick red shroud. This will wipe out solar powered equipment, necessitating the use of alternate energy sources as a backup.

When the dust on Mars settles, the sun returns—but at only half the size as it appears on Earth.

Then there's Olympus Mons, an active volcano that dwarfs our greatest mountains. Being a shield volcano with gently sloping sides, an observer on the ground can't see the entire profile, even from a distance. In other words, Olympus Mons is so big it curves visibly around the planet.

Illustration of size comparison between Olympus Mons vs Mauna Kea vs Mount Everest

Olympus Mons is a whopper volcano that curves visibly around the planet.

The Martian atmosphere is 100 times thinner than ours and is comprised of 95% carbon dioxide (vs our 0.04%). The rest of Martian air is made up of argon, nitrogen and 0.02% oxygen (vs our 21%). So without specialised breathing equipment and oxygen supplies, the colonists of Mars would quickly suffocate. The short term solution will be to extract oxygen from the plentiful supply of carbon dioxide in the Martian atmosphere. This can be filtered into the habitats and resupply breathing apparatus.

Mars is pretty chilly. The thin atmosphere means Mars can't retain heat or moisture, and levels of UV radiation are high. Temperatures are cold, averaging at -63°C (-81°F) compared to our comfortable 14°C (57°F). Summer at the equator reaches daytime highs of 20°C (68°F), dropping to -73°C (-99°F)by nightfall.

Graph of Earth Temperatures vs Mars Temperatures

The average temperature on Earth is positively mild compared to Mars.

So, while Mars is relatively "nearby" and "similar" to Earth in the grand scheme of the universe, colonising the red planet poses tremendous challenges. Check out the National Geographic series Mars for a science-based dramatisation. They seemingly overlooked the gravity issue, instead exploring the logistical, political, psychological, and biological hazards of setting up camp on Mars.

This scenario is fast becoming a reality. The race is on for governments and private companies to take humans to Mars within the decade.

"I'd like to die on Mars. Just not on impact." - Elon Musk

Colonising The Solar System

Besides Earth and Mars, our solar system contains six other planets and 180 moons which are being evaluated as homes from home.

Between us and the sun lie Mercury, Venus and Mars. They're similar to Earth because they're rock-based, and so earn the title of Terrestrial Planets. The rest of our solar system is made up of the Jovian Planets, including the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune.

Illustration of the solar system: Terrestrial vs Jovian planets

Which of the planets and moons in our solar system might one day support human life?

Mercury is a Hot Mess

The closest planet to the sun, Mercury orbits at an average distance of 58 million km (36 million miles). This makes the surface heat and radiation extremely intense: temperatures reach 426°C (800°F) by day and -173°C (-280°F) by night. Even a lead-based sunblock would melt off your face, so Mercury probably isn't a goer for humanity.

Venus Isn't Inviting Either

Venus orbits further out from the sun at 108 million km (67 million miles) but is still too hot for us to handle. Day or night, north or south, the surface temperatures are an even fiercer 460°C (860°F) on this hell ball. That's because its thick carbon dioxide atmosphere traps the sun's heat, creating a souped-up greenhouse effect.

Jupiter Would Crush Us

To date, nine spacecraft have travelled to Jupiter, sometimes using its gravity as a slingshot to further flung destinations. They've delivered some amazing images and scientific insights, showing that Jupiter is not at all an Earth-like planet.

Jupiter is the largest planet in our solar system, with a mass 2.5 times greater than all of the other planets combined. Its atmosphere is so thick it literally crushes our probes with its pressure. We do know, however, that beneath the atmosphere, Jupiter becomes liquid, and then solid. There, pressures are 50-100 million times that of Earth's pressure at sea level.

Illustration of what's inside Jupiter: gas hydrogen, liquid hydrogen, metallic hydrogen, and an iron core

The gas, liquid, and solid layers inside Jupiter.

Jupiter doesn't rotate like the terrestrial planets. Made up of mostly hydrogen and helium gas, it spins faster at the equator than the poles. In fact, it has the fastest rotational speed in the solar system, producing 10-hour days and winds of 480km/h (300mph).

Its famous Great Red Spot is a continuously spinning storm, first sighted in the 17th century. The storm itself is more than twice the size of Earth, and marks an area of super high pressure.

All in all, Jupiter looks pretty inhospitable. But don't forget its moons. Jupiter has 69 moons, the most famous of which are Europa and Callisto.

Europa is Cold But May Support Life

So far, eight spacecraft have visited Europa and photographed 15% of its surface at a decent resolution. Europa is smooth and lacks craters because of the ocean currents that continually recycle the ice.

Naturally, there's a significant chill factor. The average temperature on Europa is -160°C (-256°F) at the equator and -220°C (-364°F) at the poles. Ice quakes pose a hazard, as do the sudden explosion of violent water plumes from the icy ground.

The same side of Europa always faces Jupiter on its 3.5-day orbit. With no atmosphere, the opposite face is bombarded with deadly radiation so that's best avoided. The gravity is 13% that of Earth's, and the sky is always as black as night.

Despite all this, scientists reckon the ocean beneath Europa's ice crust could harbour alien life. NASA has funded the initial development of a number of high-tech concepts including the amphibious squid rover designed to explore the deep and chilly oceans.

Illustration of NASA's amphibious squid rover on Europa

NASA is contemplating an amphibious squid rover to explore the ocean beneath Europa's ice crust.

Callisto May Also Host Chilly Life Forms

Callisto is another ice moon, but distinguishes itself as being the most heavily cratered object in the solar system. The lack of weather and geological activity means these craters never disappear.

We may one day find this chilly moon also supports an ocean of with cold-tolerant life forms. The possibility is an enticement to set up a human base on the surface.

The Search for Distant Planets

As we travel outward through the solar system, Mars looks pretty decent. But this is just our local neighbourhood. What if there are Earth-like planets orbiting different suns? Could we one day colonise those?

In 2009, NASA launched a space-based telescope called the Kepler Space Observatory to get a better look at the skies. It has since identified hundreds of new exoplanets, including some that might be a lot like Earth.

Cartoon illustration of NASA's Kepler Space Observatory searching for Earth-like exoplanets

NASA is actively searching for Earth-like exoplanets that could support life.

This is a promising find, resulting from just a partial scan of only 0.25% of the night sky. It's partial because Kepler can only identify exoplanets when they pass directly in front of their suns. Their transit creates a tiny dip in solar luminescence, providing us with the tell-tale sign of a planet in orbit. Planets that don't make any transits are simply invisible to us for now.

The prime candidate so far is Kepler-186f, some 490 light years away. If you consider that the fastest space probe, Voyager 1, travels at 61,000km/h (38,000mph), then our best planetary candidate to date has a journey time of just over 9 million years. Even if that journey were possible, the species that steps onto Kepler-186f will drastically different from the ancestral species that departed from Earth.

Cartoon of future humans arriving on an alien planet

By the time we get to Kepler-186f we'll have evolved into a new species.

But who knows what space technology will emerge to transport us to other worlds in future. With an estimated 11 billion rocky planets in our galaxy, we're certainly not short of options.

For the first time in 3.8 billion years, life on Earth has the ability to explore other planets. This is not only a giant leap for mankind, it's an advancement for all life that we take with us. Plants, bacteria, and fungi all fuel our life-supporting ecosystems on Earth and will be vital to our long term survival on other worlds.

One we hammer out all the issues—and there are a lot of issues—going multiplanetary will be on the cards for millions of people, many of which are already alive today.

Becky Casale Author Bio

Becky Casale is the founder, keyboard smasher, and drinks lady at Science Me. She's a BSc undergrad and the mum of two catastrophically awesome critters.