Intelligent Machines are Watching Earth

Sending crewed missions to other stars is difficult and expensive. And relying on delicate and unpredictable elements such as biological lifeforms is more often than not going to lead to failure. It would be far better to send artificial 'life' - a synthetic intelligence - that could plan its own observations on arrival, making judgments based on what it finds. It would need none of the messy and error prone life support systems that biological life requires.

When this is considered it does seem to be the most likely means by which an extra-terrestrial civilisation would explore our Solar-System, especially when the huge distances and timeframes are taken into account. It would certainly be the simplest means of exploration. Given the age of the universe there are likely to have been many technologically advanced civilisations that developed long before ours. There is a strong likelihood that we have been observed in the past in this manner, and we could still be under observation now.

An alien interstellar space probe enters orbit around our sun

Such an idea is similar to the concept of a Bracewell Probe, first discussed in 1960. But unlike a Bracewell Probe, which would try to actively contact any technological civilisation that it found, I suspect in reality an alien civilisation would be much more cautious. Their probe would be hidden and undetectable, and it would watch us carefully, recording our transmissions and tracking our activities. It would then transmit its findings back to its home world, making sure such transmissions were undetectable by us.

We should be actively trying to find evidence of such probes.

If such probes are designed to be hard to find, as I would expect them to be, there will be no obvious signs of their existence. We may already have observed them directly without realising it. But the fact that they are artificial and manufactured, and highly technological in nature, will eventually betray their identity. And as they are highly likely to be self-replicating machines, there will be many of them. Once we find one many others are likely to be found soon after.

Alien probes may well be organic in appearance, and hard to identify

How such a probe will react when discovered is unknown. Will it attempt to flee, or self-destruct in a violent manner? I think either is unlikely. I think the following series of events will happen:

• The probe will alert other probes in its vicinity that it has been compromised.
• It will transmit to them the data of its observations.
• The probe will then render itself inoperable, wiping clean it's memory, and even its programming. Its artificial intelligence - its mind - would be rendered inert.
• The other nearby probes that had been alerted would inform their creators on their home world of what has happened.
• Those probes would then continue their observations as before.

If that series of events occurred we would still be able to examine the physical construction of the probe, but we would not be able to learn anything about its most important qualities: what it knows, where it comes from, and how it thinks. We would have to find a way of approaching the probe that would not trigger such a suicidal action. To do so we would have to persuade the probe that we are no threat, and to submit willingly to examination.

But how could we possibly learn to communicate with it at all, let alone convince it to cooperate with our requests?

The only way to do that would be to develop an equivalent artificial intelligence of our own. It would have to be close to the complexity of the probe's mind, and flexible enough to adapt rapidly to the probe's responses. Of course, it would have to be a very fast learner of a complex and utterly alien language (the extra-terrestrial probe would also need this ability).

We are a long way from developing such an artificial intelligence, and the current fears of the potential harm such an intelligence could do to our civilisation has the potential to hamper its development. It's a valid fear, but despite that fear such technology needs to be created. The development needs to be very carefully monitored and controlled, of course, if we are to avoid rendering our species irrelevant to superior artificial minds. We could achieve this by developing very specialised artificial intelligences that are only suitable for specific tasks, rather than artificial general intelligence (where the artificial intelligence can perform the same intellectual tasks that humans can), which should be avoided.

But why should artificial general intelligence be avoided?

One idea I find interesting, and a bit unsettling, is that intelligent extra-terrestrial probes may actually be the primary 'life-form' on their home planet. After a civilisation develops an advanced artificial intelligence, that intelligence eventually starts to improve on itself at an ever increasing rate, soon surpassing the intelligence of its creators. Such an event is known as a technological singularity. Soon the creators (the biological life-forms that built the initial artificial intelligence) do not have the ability to even understand the rapidly improving artificial intelligence. Its complexity and ability is beyond their comprehension. The artificial intelligence becomes the dominant 'species' on the planet, and eventually sets out to explore and colonise neighbouring star systems and beyond. Its creators become, at best, second class citizens, or at worst, extinct.

An extra-terrestrial civilisation where artificial intelligence is the dominant life-form

We should certainly push ahead with the development of sophisticated artificial intelligence, but as I stated earlier it should never be given the general intelligence ability of humans. It should be specialised for health care, engineering, exploration, construction or any other specific tasks we require to progress, maintain and expand our biological human civilisation.

And it certainly should be developed to facilitate communication with extra-terrestrial interstellar probes that are quite possibly watching our planet right now.

Dinosaur Civilisation

I've often wondered: if a dinosaur civilisation developed would there still be evidence of it? If there is then we would have found it by now, wouldn't we?

Not necessarily.

If there was a dinosaur civilisation it would have ended at least 65 million years ago when climate change and the asteroid impact caused the major extinction event that killed off half of all life on Earth, including all of the non-avian dinosaurs. After so much time there would be very little of their civilisation left for us to find.

A decade after the asteroid hit

Artifacts

Amazingly, there are artifacts found in coal seams that could be evidence of a dinosaur civilisation. Coal takes 30-300 million years to form, so anything found within it must fall within that age range.  A gold chain and iron pot have been found in such seams, but the most interesting by far is a bell with a handle. The coal seam in which it was found is said to be up to 300 million years old, which would place it in the early part of the dinosaurs' reign. The bell was examined at the University of Oklahoma. It was found to contain an unusual mixture of metals, quite different from any modern usage.

The most intriguing feature of the bell is the figure on top of the handle. The figure's face is certainly not human.  Instead it looks like it could be reptilian, or avian in nature (the small wings make the avian link much more likely).

The figure on top of a 300 million year old bell handle - a sentient dinosaur?

It could be that when we look at the face of that figure we are looking at the likeness of an intelligent dinosaur, one of high-importance to its civilisation: perhaps an emperor, a great priest, a famous historian or philosopher, or a warrior. It could even represent a deity. That is quite a profound thought.

It's sad to think that thousands of such artifacts may have been destroyed in the furnaces of power stations around the world. Ideally coal mining facilities should be updated to detect metallic artifacts before the coal is transported away. If that was done we could soon find conclusive evidence of a pre-human civilisation that once thrived on Earth during the time of the dinosaurs.

Intelligence

The fossils we have found show us just a small percentage of dinosaur species. Fossilisation is a rare process indeed, and fossils of the intelligent dinosaurs that could have created such a civilisation may never be found.

Dinosaurs certainly had ample time to develop intelligence and civilisation. Humans have only been around for about 1.6 million years, and it's only about 4 million years since our ancestors first stood upright. Human civilisation developed only 10,000 years ago. Dinosaurs were the dominant lifeforms on Earth for 165 million years. The limited fossil record shows an incredible diversity of dinosaur species, each adapted to specific roles and environments. It seems likely to me that in all that time there should have been at least one dinosaur species that evolved intelligence to a similar level as our own, especially when you consider the brains of their direct descendants: birds.

The face of an intelligent dinosaur

In general the dinosaur fossil record shows that dinosaurs had small brains, but recent studies show that bird's, the descendants of dinosaurs, have much more intelligence than previously thought. Their brains have neurons that are much more densely packed than those of mammals.  In fact, some relatively small birds can have a similar number of neurons to primates. Theropods, the dinosaur ancestors of birds, were present throughout the reign of the dinosaurs, from the early Triassic to the final days of the late Cretaceous. Like birds, their brains, although much smaller than human brains, would have contained a much denser collection of neurons. It's possible that they could have reached a similar level of intelligence to our own with a much smaller brain than ours. The smaller brain size could even have lead to faster thought and reasoning processes which could have hastened the development of civilisation, and possibly to an even higher degree than our own.

There is a remarkable amount of evidence already found within coal and rock that suggests civilisations existed on Earth long before modern human civilisations developed, with some discoveries even hinting at advanced technology. I suspect that the most astonishing discoveries are yet to be made.

Perhaps we will one day find evidence of a space-faring civilisation that existed on Earth millions of years ago, one that managed to send some of its population away on an interstellar voyage to escape one of the many mass extinction events that have plagued our planet. The descendants of that civilisation could be living quite happily right now on another Earth-like world many light-years away.

And they could be dinosaurs.

Where Did All The Martians Go?

Mars is arguably the only place in the Solar-System, other than Earth, where intelligent life could have developed. There is a lot of evidence to indicate that Mars once had a much thicker atmosphere, with a significant surface ocean of water. If such ideal conditions for life existed for a billion or more years then it's possible that a technological civilisation developed.

Mars as it looked a billion years ago, before the decline of its atmosphere, climate and civilisation

But what happened, and where did all the Martians go?

A while ago I wrote about the evidence of a nuclear war on Mars, a war that devastated the entire planet's delicate ecosystem millions of years ago.  With its atmosphere and environment already in severe decline, and its oceans almost gone, the war was the fatal final step towards rendering the planet uninhabitable.

The ruins of a Martian city a few centuries after the final war

The survivors, providing they were technologically advanced enough, would have had only two choices: retreat underground, or evacuate to space.

I suspect that both choices were taken.

Mass Evacuation

Astronomers on Mars, much like on Earth, would have long been interested in finding similar planets to their own in other star-systems. And at least a few would have been found. With the knowledge that their own planet would soon be uninhabitable I expect plans would have been put into action to ensure the survival of their species. Over many centuries the Martians would have launched thousands of missions into space, and created colonies in the asteroid belt with the sole purpose of constructing a fleet of generation ships capable of sending tens of thousands to the planets they hoped they could settle on.

As each generation ship was completed thousands of Martians would have boarded and been launched on an interstellar journey, a journey that would have taken tens of thousand of years, and hundreds of generations, to complete.

One of the mysterious bright spots on the Ceres asteroid . Could this be evidence of previous or on-going Martian mining activity for interstellar spacecraft construction?

It is likely that dozens of such generation ships would have started on such journeys before that final war rendered the surface of Mars truly uninhabitable. Some of those ships would have reached their destinations. It is quite possible that there are now several flourishing colonies of Martians within a few tens of light-years of our Solar-System.

Deep Underground

Despite the exodus of tens of thousands into space, the majority of Martians would have had to remain on Mars. With the surface rapidly becoming uninhabitable there would have been no choice but to build vast underground cities with the ability to sustain populations of millions almost indefinitely. This would be an impossible task on a dying planet, but a subterranean facility suitable for a million or so could succeed. While millions would have perished as the final desperate war was fought, at least a significant population could be maintained far below the surface, ready to eventually leave Mars when the possibility arose.

Is that huge underground haven on Mars still occupied? Or has it been abandoned? There was evidence seen not long ago that could have been recent launches, perhaps shuttles on their way to the asteroid belt to join one of the last generation ships.

Could we have already witnessed the final evacuation of Mars?

The entrance way to a long abandoned underground Martian city

If we have then there will be at least one huge abandoned underground facility that could be used by human colonists. It's something that we should be actively looking for.

We need to be doing the following:

• Searching for evidence of Martian colonies on planets around nearby stars.
• Exploring the regions of Mars where the entrances to the underground cities may be located, perhaps near the larger subsurface water deposits, or near the poles. We need to be careful, as Martians may still be living there.
• Excavate the ruins of Martian surface cities to learn about their culture, technology, and if possible obtain clues as to where their generation ships have gone.
• Send probes to the asteroid belt to uncover evidence of the Martian interstellar shipbuilding activity.

Possible remains of a Martian surface city, taken by NASA's Mars Global Surveyor

There is so much to learn about this fascinating planet. It is quite possible that the secrets of a once flourishing technological civilisation are lying just beneath the surface. The tantalising evidence of ruined cities should be the target of manned archaeological expeditions as soon as a permanent human presence is established on the planet.

Once humans arrive on Mars I would expect to see a deluge of sensational discoveries.  We could find that we are not the first advanced civilisation to evolve in the Solar-System. Such a discovery will force all of us to reconsider our place in the universe. And it will provide humanity with a supreme motivation to embark on interstellar exploration at last.

Self Destruction: The Greatest Risk to our Species

The are many possible ways that our civilisation, and our very existence, could end. There are those beyond our control, such as asteroid strikes, hostile extra-terrestrial action, and even vacuum collapse (which may actually destroy the entire universe), but those are highly unlikely. The most likely extinction events for humans are those that we can bring upon ourselves.

And within the next century or so, such an event is looking highly likely.

Climate change will make some areas, such as much of Africa and the Middle East almost uninhabitable due to heat and drought. That, combined with the political situation in such regions, will result in wars over water and food. Millions of people will migrate north, putting huge strain on Europe and even Russia where water and food will still be relatively plentiful. The result could be the use of lethal means to protect resources. With North America also inundated the risk of global conflict, and the likely way such a conflict would escalate, would increase dramatically.

Will this be the last technological act of our civilisation - its self destruction?

The stress on the planet due to climate change, resulting in a global war with nuclear and biological weapon exchanges, would remove any chance for humans to embark on an interstellar colonisation effort. Those that remained would be trapped on a poisoned, starving, disease-ridden world, where all their thoughts and energy would be devoted to the task of surviving each day. It could take thousands of years for another technological civilisation to develop. With human nature being what it is, any new civilisation is likely to repeat the mistakes of the previous ones.

The effects of climate change could lead to nuclear war

Those born today could be the last generation to born into a technological human society, unless something is done now to safeguard ourselves and our knowledge from self destruction. And that final apocalyptic step could well be the usual final step for a civilisation such as ours, given the apparent lack of technological civilisations in our galaxy.

The final hours of our civilisation mapped out on giant screens in command bunkers

It is interesting that, despite extensive efforts, no technological extra-terrestrial civilisation has been detected. Why is this?  That is the question posed by the Fermi Paradox, which wonders why, given the age and size of the universe and all the billions of stars and planets that exist (or have existed), we have not yet detected any other extra-terrestrial civilisations. There should be an abundance of alien technology out there, and some of it, such as a Bracewell Probe, should have reached our star system.

There are many possible answers to this, but many consider the self-destruction answer (the great filter hypothesis) the most likely.

Once a civilisation develops the ability to destroy itself, it will.

That is a chilling prospect.

It is possible that such a stage in a civilisation's development is insurmountable - there is no way, once a civilisation develops the ability to destroy itself, to avoid using that ability. A civilisation simply does not have the time to safeguard its species beyond its home-world before it brings on its own extinction.

The ruins of a long dead alien civilisation - one of millions?

Those of us alive now are living in a pivotal moment of human history. We have the technology and ability (or almost do) to begin to move away from Earth and secure the future of our species among the stars. And we have the technology and ability (with certainty) to destroy all that we have achieved and send our species into oblivion.

There needs to be a massive political and social change in our world if we are to get through this seemingly insurmountable moment in our history. Governments need to set aside their petty squabbles. If that can be done we may well be one of the first, or one of the few, technological civilisation to progress to the next stage. And if that is indeed the case, we will be joining a very select club of civilisations.

We have a century, possibly only a decade or two, to ensure our membership.

Let's not blow it...

Immortal Travellers

Unless a faster-than-light means of propulsion is developed, which is looking extremely unlikely, voyages to other star-systems will at best take centuries. For a crew of normal humans this would mean that those that left Earth would be long dead by the time the ship reached its destination. Only their distant descendants, after many generations had lived and died in the depths of interstellar space, would be alive to see the ship's destination.

A generation star-ship under construction in Earth orbit

Such a 'generation' ship may well be the only way humans could reach and colonise other star-systems. It would need carefully automated management of the human occupants to ensure that each generation is content enough to minimise the chances of conflict and mutiny - the occurrence of which would almost certainly doom the entire mission, and be fatal for everyone on board.

A generation 'worldship' capable of sustaining ten thousand occupants

The management of each generation would need to vary quite dramatically depending on which point of the voyage they were alive:

The Launch Generation

The initial occupants, born and educated on Earth, would have full knowledge of their origins, and of their fate on board the ship. This would be the generation most likely develop the psychological and behavioural problems that could endanger the ship and its mission. There would be no opportunity to return to Earth, and the longing to return to the space and luxury available back on the home world may become too much for a significant number on board. The crew for this generation would have to be selected very carefully indeed. Fortunately, this would be the one generation that could be monitored from Earth and a relatively timely response to problems given.

The Interstellar Generations

The first generation born on board, and all those born during the centuries-long voyage, would live in what I would call the 'planned ignorance phase'. They would be taught nothing of their origins, or their ship's ultimate destination. They would not even be taught that they are on a voyage. The ship's education systems would ensure this. They would be taught mathematics and language skills, and all the skills required to survive on board and maintain the ship, but nothing more. This would be crucial to reduce as much as possible the risk of unrest and rebellion. Enforced ignorance, however unethical and even cruel it may seem, would be important during the interstellar phase of the mission.

The Colonisation Generation

Only the final generation will leave the ship to set up the colony on the destination planet. They will be the first humans to experience life outside the ship since the launch generation (now their distant ancestors). The ship's education system would reveal their origins, the purpose of their mission, and what will be required of them. They will be the first to have free access to the vast knowledge store that was secured by the launch generation centuries before. So long as this explosive phase of education is started from birth it should instill a strong sense of purpose and adventure in the colonisation generation, and a sense of pride that they are that final ship-born generation. That should be enough motivation to give the crew the best chance of success down on the surface of the destination planet.

With careful design, the process of controlling the generations stages detailed above could be automated to a high level, with an artificial intelligence looking after all aspects of life support and maintenance, and directing the occupant's activities accordingly.

But there is an even better way to do this, and one that would, in my opinion, increase the chances of a successful colonisation mission, and reduce the risks of the occupant's society devolving to a tribal or even feral level, from which recovery would be almost impossible.

The Permanent Generation

It would be better to have on board a small team of humans that could oversee the generations, and that could adapt the running of the ship to circumvent any unforeseen events that are likely to arise. The 'permanent generation', as I call them, would have undergone life extending treatments before leaving Earth, rendering them biologically immortal.

An immortality treatment facility

This is not as fantastic a concept as it may first seem. Research is beginning to show that life-extending genetic treatments should be possible, and recent news reports suggest that the first such treatments could even be available within decades.

Such an immortal crew would be far fewer in number than the mortal occupants, perhaps no more than ten percent of the total, and they would need to be treated very differently:

• The immortals would need to be segregated from the mortal occupants, with no physical or visual contact between them. The mortals would essentially have no idea of their existence, which would be necessary to avoid envy and a reason for mutiny and rebellion, or even religious adoration.
• Due to their immense lifespans the immortals would need a lot more living space per person, compared to a mortal human. And that living space would need to offer a high degree of luxury and the stimulation of intellectual pursuits to maintain their physical and mental well-being.
• The immortals would have full access to all the knowledge from Earth, and of their mission, unlike the mortals who would spend most of the voyage in the 'planned ignorance' phase.
• Only the immortals would be able to look beyond the confines of the ship to allow for astronomical observations to be carried out - an important intellectual activity, and important for the mission's success.
• The immortals would be in contact with Earth at regular intervals. This would be in direct contrast to the mortals, who would, after the launch generation had died, not even have knowledge of their origin.

The spacious communal area for the immortal crew

I believe that such a combination of a mortal and immortal crew on an interstellar colonisation mission is essential for a conventional spacecraft. Until we can harness the vast energies of antimatter, and develop suitable containment methods for it, such missions will take many standard lifetimes to complete.

We should not delay such colonisation missions until faster-than-light travel is developed. If we do it may then be too late to begin. The continuation of our species is the primary objective, and the longer we wait before launching missions to other star-systems the more chances there will be for us to be wiped out by a major catastrophe.

We are within a century of being able to build and launch a generation star-ship, and within decades of immortality treatments.

Such a mission should already be in the planning stages, and it should launch within the next century or two. Time is running out much faster than most people realise.

There is a new epic and thought-provoking short novel called 'The Immortal Kings', available at Amazon, about such an interstellar mission with an immortal crew element. It's well worth reading.

Building Vast Colonies in Space

We should, at the very least, have an orbiting and functional prototype of something like this by now:

Kaplana One Space Settlement - design study in the early 2000s

Pictured above, the Kaplana One Space Settlement is a 500-metre diameter habitat designed to accommodate around 3,000 people on its inner surface. Inhabitants would experience simulated gravity the same as Earth's when Kaplana is spun up to about two revolutions per minute. The interior would consist of large open spaces with grassland and lakes as well as housing, creating a very pleasant environment to live and work. It's a remarkable design, and could be built with existing technology.

Kaplana One Space Settlement - interior

The first Kaplana space settlement will be an enclave of the super-rich, judging from its design. And that’s fine – it’s a great way to recover initial development costs, and a way to generate interest in developing an interplanetary economy, rather than space being nothing more than a place for scientists. It will also encourage the general population to view living in space as desirable rather than as something to be endured.

Asteroid mining is likely to be the first economic activity beyond the confines of the Earth. And such mining will be needed to construct space settlements.

Moving an asteroid ready for construction activity

The second Kaplana-style settlement is likely to be a comfortable accommodation centre for asteroid mining staff. Instead of the spacious homes, gardens, golf courses and lakes of the first one, there are likely to be multi-story accommodation blocks (and individual houses for senior staff, perhaps). The accommodation would still be spacious compared to anything the first asteroid miners are likely to experience, and there would be plenty of recreation space. And, of course, the simulated Earth gravity would keep the mining staff healthy and strong. Such a settlement would be hugely preferable to cramped and almost zero-g habitats on the surface of asteroids.

Construction of a space settlement for asteroid miners

It’s quite possible that if the first Kaplana-style space settlement is successful that most of the initial decades of asteroid mining activity (even centuries) is devoted mainly to building such desirable off-world habitats, and the infrastructure that goes with it (luxurious transportation from and to Earth, supply routes with essentials such as water, microwave power transmission etc.)

It may be that there will be very little interest in building habitats on planets and moons in the Solar-System. Space habitats may well become the preferred places for humans to settle, and become the best means to preserve our species. One of the main reasons for this will be the relative ease at which Earth gravity can be simulated. Simulating such gravity on the Moon, Mars, or any of the other solid worlds in our Solar System would be almost impossible. Long-term colonists on those worlds, and especially their offspring, would be doomed to remain there, their weak bodies unable to cope with a gravity environment even half that of Earth.

With this in mind, the best way for humans to explore the surfaces of our Solar System's planets and moons would be for mobile Kaplana settlements to visit those worlds and for short excursions to the surface to take place. Permanent bases could, and should, be built, but the crews should be rotated on a regular basis so they could return to a comfortable, spacious and high gravity environment. This would ensure that their physical and mental health was maintained. With a permanent route with numerous Kaplana settlements journeying out to Mars, the asteroid belt, Jupiter, Saturn etc., and then back to Earth, miners, scientists and others could make the journey (albeit over many years) in comfort and relative safety, disembarking to surface colonies for a while, and the leaving to join the next Kaplana settlement that comes by. Or, they could return to a settlement that is in permanent orbit for a month or two to recover their strength before returning to the surface. Smaller spaceships, with torus-style rotating sections, could be used for the shortest routes, such as the one below:

A small spaceship with rotating sections - ideal for shorter resupply routes e.g. to the Moon or Mars

Building such a network of Kaplana-style space settlements does seem to be one of the best ways to ensure the short term survival of our species.

Of course, for longer term survival (millions of years instead of thousands) interstellar ships will be required to colonise other star-systems. The design of such ships would benefit greatly from the lessons learned while constructing Kaplana-based settlements. No matter how long the voyage, a gravity environment is essential if the generation that will make planet-fall is to have the best chance of success. Indeed, even a super-Earth, with it's high gravity, could be colonised if the spin rate of the interstellar ship was slowly increased during the voyage to simulate the conditions on the target planet. The humans on board would adapt to the higher gravity well before their destination is reached.

Until a suitable planet is found with conditions almost matching the Earth, living in such space settlements does seem to be the next best thing.

Kaplana is an improvement on some space settlement designs drawn up in the 1970s. They were impressive studies, particularly the Bernel Sphere, a 500 metre diameter sphere for up to ten-thousand inhabitants (actually first proposed in the 1920s), the O'Neill Cylinder, an 8-kilometre wide and 32-kilometre long cylinder, and last but not least the Stanford Torus, an almost two-kilometre diameter ring.  All would rotate to simulate Earth gravity.

O'Neill Cylinder - one of the impressive space colony designs of the 1970s

I know I'm restating a point here, but it's remarkable that not even a small test version of any of the designs has yet been built.  They are all possible with today's technology, and any one of them would be an ideal first step to ensuring the continuation of our species when the inevitable global extinction-level event consumes life on Earth.

Living on Rogue Planets

Most planets are gravity-bound to a star. But there are many that are not. Known as rogue planets, or free-floating planets, they inhabit the region's between the stars, bound only to the gravity of the galaxy as a whole. Such worlds are dark and cold, and it would seem at first thought that they would be unsuitable as a destination for colonisation.

But indigenous life could evolve even there, which means that humans could survive there, too.

A rogue, or free-floating, planet with a small moon

Rogue planets could be of any type, from gas giants to small Earth-sized world's of Rock and ice, and it would be those smaller planets that would be of most interest. If a thick enough layer of water ice were present, a subsurface ocean, like those found on some of the moon's of Jupiter and Saturn, would be a strong possibility, kept warm by geothermal vents in the rocky core. The nutrients flushed out could provide a stable environment suitable for simple life to form. And it could provide an environment to sustain and feed a human colony.

A view of a nebula from the surface of a rogue planet

Another type of rogue world, blanketed in a thick hydrogen atmosphere, could also be suitable for colonisation. In such a cold environment such an atmosphere could be sustained on a relatively small rocky planet, and the insulating effect of the gas would keep the surface temperature above the freezing point of water. This would allow lakes and oceans to form. If the planet remained in this state for long enough it is entirely possible for life to evolve, once again fed by the nutrients of volcanic activity from the core.

Of course, such a thick atmosphere would create surface pressures that would be difficult for human colonists to deal with, and the perpetual darkness would present it's own issues. Power generation would need to nuclear, and eventually geothermal. There would be psychological issues, too. Humans evolved in a sun-drenched environment. Such an environment could be simulated, though, and the experience would be no different to that experienced on a generation ship on its centuries-long voyage between stars.

Colonists arrive on a hydrogen 'blanketed' rogue planet

Now that we've established that colonisation is possible on such worlds,  another question arises: why would we want to do it? Such dark, cold and remote planets seem to offer little that is desirable as a place to live. They seem positively undesirable.

But when we consider them with regards to the survival of our species such remoteness becomes highly desirable indeed. And this is why:

• Rogue planets are generally a light-year or more away from the nearest stars, greatly reducing the chances of being hit by lethal solar events.
• Without the debris of rock and ice associated with solar systems, the risk of a catastrophic impact is almost completely removed.
• An advanced and predatory extra-terrestrial civilisation is more likely to overlook, or even not notice, such planets, offering humans a higher chance of surviving should such a civilisation ever become aware of our existence on Earth.

Intelligent extra-terrestrials examining data on their latest discovery: Earth...

Transporting a colony to a rogue planet is the main hurdle to overcome. It would be hard to justify sending a large ship of colonists that would then have to decelerate deep in interstellar space and become trapped in the gravity well of such a planet. But when large generation ships do eventually leave to colonise worlds around other stars, it would be relatively easy to incorporate smaller ships into the design that would be despatched enroute. With just a couple of hundred carefully chosen occupants a viable colony could be established.

Such colonies, as hard as they probably would be to build, may well become the most sustainable and successful, having overcome some of the most extreme challenges possible.

Indeed, such colonies, and the skills that they would learn, may well be the only way to ensure the continuation of our species beyond the general heat death of the universe.

Nuclear Propulsion - Why Aren't We Using It?

We need to establish a permanent human presence beyond Earth. But it's not easy with the expense and slow nature of our current space flight capabilities using chemical rockets, and of course their poor payload capabilities. But there is a method of propulsion that we could develop with today's technology, one that has the strong potential to allow us to colonise our solar system in decades rather than centuries. That is, of course, nuclear propulsion.

Why has it not already been developed?

The idea of using atomic bombs as a means of propelling spacecraft is an old one, first put forward in 1946 by Stanislaw Ulam. He proposed using small nuclear explosions to accelerate a spaceship, an idea that underwent serious study in the late 1950s under the name of Project Orion. It's a remarkably simple idea: a rapid series of detonations behind a protective pusher plate would accelerate the spacecraft, with shock absorbers evening out the acceleration effect on the crew.

Design for a modern Project Orion spacecraft, with a close-up of the crew section

If one-gee acceleration was achieve the crew would experience normal Earth gravity. Ideally, such acceleration would be maintained until the mid point of the journey, after which the spacecraft would be turned and decelerated at the same rate.  This would provide the equivalent of normal gravity for the crew for the entire trip, eliminating the negative health effects of zero gravity.

Such constant acceleration would make interplanetary travel within our solar-system incredibly swift. When Mars is at its closest point to Earth, only 65 million miles away, it would take just two days for the acceleration and deceleration phases at one gee. For Jupiter and Pluto it would take about 6 and 11 days respectively. Those are phenomenally short journey times, all quite achievable with technology available to us now.

A Project Orion spacecraft leaving Earth orbit, and arriving at Mars two days later

The use of such a large amount of nuclear detonations means that launching from the surface of a planet is not feasible - the radioactive fallout produced would be unacceptable in all locations, and the electromagnetic pulses would damage sensitive electronics in line of sight with the launch. Such a spacecraft would have to be constructed in orbit and their nuclear detonation drive activated only when a safe distance from Earth had been achieved.

Project Orion had such incredible potential, but the political will was not there, mainly due to concerns about fallout, and that, incredibly, no one in the US government at the time could see a point to having such a massive launch capability. The project died in the early 1960s, with the US government no doubt wanting to put all it's investment into getting a man on the Moon. To have such an incredible lack of vision is quite astounding.

That was not the last of such projects.  A decade later the British Interplanetary Society conducted a study under the name of Project Daedalus. The propulsion system studied was a fusion rocket, which would detonate hundreds of pellets of a deuterium/helium-3 mix.  Helium-3 is rare on Earth, but fortunately it is relatively abundant on the Moon making that location the ideal one for constructing and launching such a vehicle.

A Project Daedalus two-stage interstellar spacecraft

The project focused solely on designing an unmanned interstellar spacecraft that could reach its destination star system, Barnard's Star, within a human lifetime. The design, a two stage system, has the potential to reach a velocity of up to 12 percent the speed of light. Unfortunately this project has remained nothing more than a paper study.

It's disappointing that no spacecraft with a nuclear propulsion system has yet been built.  Even a recent project started in 2009, and named Project Icarus, had aims only to design an interstellar spacecraft for a potential mission in the coming centuries, and to motivate scientists in designing such things.  There are no concrete plans to build even a test system for launch.

A Project Icarus design concept for an interstellar spacecraft

Other means of rapid space travel, such as antimatter warp drives, are likely to remain in the realms of fiction for centuries, even forever. We should get over our moral objections and fears of all things nuclear. We should embrace the raw power and efficiency of such a means of propulsion, and get building and launching such spacecraft now. It may well be the only technical means by which we can ensure the continuation of our species.

If we do that, then within a century or two we could have flourishing colonies and economies on our solar-system's planets, moons and asteroids. With the vast resources that would then be at hand it would only be a matter of century or two more before our first interstellar colonies are established.

We need to just get on with it.