Where to start? 

First, we need to decide what ‘living on another planet’ means. A one-off visit by an expedition of astronauts is very different to an outpost regularly supplied from Earth, or a long-term colony, spanning generations, living independently from humans on Earth.

In short, a visit to another planet by a human crew is possible, but some are easier to explore than others. Each planet is different and has a unique set of challenges. For example, the largest planet in our Solar System, Jupiter, is a ‘gas giant’ mainly composed of hydrogen and helium gas. Without a well-defined solid surface, it would be nigh on impossible to set up camp there.

How about Venus? Well, Venus does have a solid surface: a good start. But its thick and dense atmosphere of (mostly) carbon dioxide (C0₂) makes the pressure at the surface ninety times higher than it is at the Earth’s surface! That’s the same as 900 metres below the ocean’s surface on Earth, and deeper than even modern nuclear submarines can access (although specialist deep-sea craft can now reach greater depths).

To make things even harder, the high concentration of carbon dioxide in Venus’ atmosphere causes a very strong greenhouse gas effect. This means that the temperature on its surface is around 460°C! A number of unmanned missions have failed prematurely in the past due to this. For example, the Soviet unmanned lander programs Venera and Vega stopped functioning within one to two hours of landing, due to the high temperatures.  

A life on Mars

So Jupiter is a no, and we can pretty much say the same for Venus – but what about Mars?  It’s the planet closest to the Earth after all. Mars has slightly lower gravity than Earth, and its atmosphere is extremely thin and consists of mostly CO2, which is poisonous to humans. Although Mars has an average temperature of -63°C, which would be very cold for humans, its highest temperature is a toasty 30 °C… This is starting to sound promising… That said, it's likely to feel pretty cold most of the time since the thin atmosphere wouldn’t offer much insulation. But in theory, a visit by a manned crew could be comparable to a visit to the Moon and we’ve done that almost 50 years ago! 

The key difference is that it takes a lot longer to travel to Mars. Instead of a roughly four-day flight to the Moon in the days of Apollo 11, any flight to Mars with current technology would take several months. NASA’s Curiosity Rover that landed on Mars in 2012 took over eight months to make the journey. 

But while this might be expensive, it’s not impossible to sustain a crew of astronauts for the flight there and back. We know from previous successful missions to the Mir and International Space Station (ISS) that humans can survive over a year in zero-gravity at a time.

Even setting up a manned outpost - similar to the International Space Station - on Mars, is a possibility. It would just be really costly, especially due to longer supply lines to Mars than to the ISS. The distance to the Moon is already about 1000 times further from the Earth than the ISS is, and Mars is over a hundred-thousand times further than the ISS. 

Panorama of the Gusev Crater on Mars

Not to forget…

There are some other key challenges to visiting or setting up camp on Mars that we should probably think about. For example, there are only trace amounts of oxygen and water vapour in the atmosphere. The low pressure on the surface of Mars (only 0.6% of the pressure at the Earth’s surface) makes it impossible for liquid water to exist on the surface of Mars without evaporating. 

Low pressure, low temperature and lack of a breathable atmosphere aren’t necessarily as bad from the point of view of human exploration as the very high pressure and temperature on Venus. In fact, these factors are less likely to make equipment fail. But any humans settling on Mars would definitely need to live underground or in enclosed environments with artificial atmospheres and water supplies, and they would have to wear space suits to venture outside.

The poles of Mars feature lots of frozen water, and large supplies of frozen water have been found just under the surface. This means that with energy from solar cells, ice could be melted in a pressurised environment and oxygen could be produced from it using electrolysis. 

Food production would be difficult (fertilizers for growing plants would be difficult to produce, even with enough water and sunlight for plant growth), and establishing modern industries to make any colony self-sufficient would be very tricky. 

To sum, a colony on Mars is not impossible, it’s just not at all clear exactly how it would work. 

Where else? 

Planets outside our Solar System - known as exoplanets - are too far away to access using current technology within the lifespan of a human. And too far away to access using any technology we can imagine at this time.

One of the fastest spacecraft ever launched from Earth, the New Horizons probe, took 9.5 years to fly from the Earth to the dwarf planet, Pluto at the outermost reaches of the Solar System: 4.7 billion kilometres away. Impressive as that sounds, the next-nearest star (other than the Sun) is almost ten-thousand times further away! Reaching those planets with a human crew would take thousands of generations, living and dying on the spacecraft. All the supplies for the journey would have to be carried on the spacecraft, without a possibility of resupplying.

However, let’s imagine for a moment that we could get there… Several exoplanets in the ‘habitable zone’ (the right distance from their star to support liquid water and potentially life forms) have been identified. We just don’t know much about the conditions on them compared to the planets in our Solar System so it's difficult to assess their suitability. To learn more about exoplanets, have a listen to Dr Ruth Angus (Columbia University). 

To conclude, any new human colonisation on another planet would be very difficult. The extreme weather conditions, the chemistry of the atmosphere and the vast amounts of resources needed to support human life all play into this. But who knows what the future holds as our technology advances? Could you imagine a human population living alongside an alien one or maybe it’s simpler to take better care of our own planet? What do you think? 
 

Are we using more resources than the Earth can provide? If so, what’s the solution? Should we try to move to another planet? Dr. Stuart Armstrong (University of Oxford) is part of an expert team that works out global risks to humans living on Earth (see the Global Catastrophic Risks 2017 report). He says although this is a difficult question to answer, there are ways for us to continue living on this planet if we adapt.

Drinking seawater

You might be surprised to find out that it’s not the essentials - such as water running out - that threatens human life on earth. In fact, Dr. Armstrong explains that: “We could have enough food, water and energy for the whole human race for the foreseeable future and at reasonable costs. Take water… most of the world’s water is seawater. The worst thing we’d have to do is get all our water from the sea! But there’s plenty of it. We’d have to remove the salt to make it drinkable [in a process known as desalination] but this is feasible”. 

“Now let’s look at food. The ultimate way of producing food would be by growing plants in greenhouses without soil - this is called hydroponic growing. We’d use much less water growing food this way which would lead to a huge decrease in water use,” he says. 

The power of the sun 

When thinking about how long we can survive on Earth, another big issue is energy - heat, light and fuel to transport people and goods around. What will happen when our supply of fossil fuels (oil, gas and coal) runs out or becomes too difficult for us to get out of the ground? “We could replace our current energy sources [with renewable ones such as hydro (water) or solar (sun) power]… using solar panels at current prices would mean spending only a tiny bit more than we currently do,” suggests Dr. Armstrong. There would have to be solar panels everywhere and they would need to be well looked after to ensure they always worked. But this is doable.

“The world has a lot of problems but lack of basic resources isn’t one of them,” says Dr. Armstrong.

Meteorites and medication

So if lack of food, water and energy isn’t the biggest risk to human life on Earth, what is? What about an strike from meteorites…like the one which is said to have made the Earth unlivable for the dinosaurs? The National Aeronautics and Space Administration (NASA) space station in America funds several survey teams to look out for meteorites. “Should an impact be predicted with sufficient warning time, several techniques are being studied that may allow successful deflection [i.e. we may be able to direct meteorites away from us],” says Dr. Armstrong. And so the risk of this happening and seriously damaging the Earth may be decreasing as we learn more about the Universe and how we can interact with it.  

When thinking about disease, you may have heard in the news about the concern that antibiotics (such as penicillin) - which help fight infections - may eventually stop working. The NHS and global health organisations are trying to reduce the use of antibiotics, especially for conditions that aren't serious. This is because their overuse in recent years means that they're becoming less effective and it’s led to the emergence of so-called "superbugs". These are strains of bacteria that have developed resistance to many different types of antibiotic.

It’s only been 76 years since a team at Oxford University proved penicillin could kill infections, can you imagine if we were to return to the days before this life-saving cure? 

“We can survive again without antibiotics”, says Dr. Armstrong. “There were ways of dealing with diseases caused by bacteria such as isolation which is how they were treated before penicillin.” [There used to be places called isolation hospitals where people went if they had a highly infectious disease]. This obviously isn’t ideal and seems like a bit of a backwards step - Dr Armstrong explains - but the point is, we could do it. If antibiotics stop working, it won’t kill off the human race.

Biggest risk to life on Earth

What then is the biggest risk to life on Earth? Well, latest calculations show that it’s us, humans! “Human-generated risks are the most dangerous, such as nuclear war, some biotechnology risks (e.g. the development of human-created microorganisms that could lead to rapid outbreaks of disease), and maybe artificial intelligence,” says Dr. Armstrong. 

If we take nuclear war, for example, this is a threat that’s existed since the end of the Second World War in 1945 and it hasn’t happened yet. A lot depends on humans (especially those in power) managing to get along with each other without falling out to the point that we mutually blow ourselves up. You could argue that if we were to move to another planet, we’d take all our human problems with us. It’s a bit like going on holiday or moving to another area... There might be a change of scenery and geography, but ultimately we’re still the same people – so we’d still have rows. 

Life on Earth could also be threatened by the growth of clever computer programs, known as Artificial Intelligence (AI)”. “If the world is changed to suit AI, it may not be compatible with human life. There is great uncertainty about AI. Could it run the world to suit itself and not humans? Or it might only be compatible with some humans, not all?” says Dr. Armstrong.

And so “We may well be able to move to another planet, but we’d need to take a lot of the Earth’s environment with us or remake it when we get there. The technology to allow us to do this is developing all the time. But why should we do this when it’s so much easier to use the same technology to continue to live on Earth? We don’t need to find another planet; we need to find a way of staying on this one and making sure we don’t blow it up!”

Reasons to be cheerful

“There are many reasons to be optimistic about the future. Right now, there are no real risks to the survival of humans on Earth. You could even say human life is flourishing as quality of life is better than ever, though some might disagree and of course, this is a big challenge in some parts of the world,” says Dr. Armstrong.

Teamwork on a global scale 

What’s most needed for human life to continue indefinitely on Earth is for people and countries to work together. This is necessary not just to prevent wars - nuclear and otherwise - but to join together on new ways of managing our environment. We can be a lot further on the way to solving life on Earth if we really want to be. It needs long-term planning and international cooperation. It means making changes to our lives now for the sake of future generations. Already some of these changes are happening, such as: charging for carrier bags to discourage the use of plastic; recycling as much as we can; travelling less; eating locally-grown food and putting on a warm jumper instead of turning up the heating! If everyone made small changes, it could make a big difference. 

There is much hope concludes Dr. Armstrong. “Renewable energy sources are reducing in price all the time and energy storage is getting better too. We’re making the problem easier to solve.”

So we may not need to move to another planet to survive after all. Are you relieved or maybe you were looking forward to living on another planet – and taking an intergalactic tour?