With 2013 scheduled to host two “Great Comets” in March and December amateur and professional astronomers alike will we gearing up to what looks to be a great double whammy. Comet PANSTARRS, a comet discovered in June 2011, will pass within 102 million miles from Earth at its closest and be present in our skies from the 10th to the 24th of March. The other is Comet ISON, discovered by Russian amateur astronomers is estimated to approach Earth at 40 million miles a month, if, that is, it survives its perihelion with the sun. Comet ISON will get within three-quarters of a million miles from the Sun before it begins to move away and continue on its path. The comet is expected to be around about 15 times the brightness of a full moon and hang to its place in the sky for a month beginning mid November.

Whenever I hear about comets or asteroids passing by our planet the question that always seems to spring to mind without fail is, “What would happen if they hit us?”
Well there is a difference between a comet and an asteroid, mainly to do with size and composition etc., but the effects that they would have on our planet would be somewhat similar. Neutron Stars, however, wouldn’t even have to directly touch us to completely devastate the planet. Whereas comets or asteroids would only release enough energy on impact to scar the Earth with craters, a Neutron Star has the power to completely obliterate it out of existence due to the immense power of its gravitational forces. Luckily for us they are a lot rarer in our galaxy than comets or asteroids.

Big impacts from NEO’s (Near Earth Objects) come once every 100 million years or so with smaller impacts much more frequent. Most are due to objects being flung from the main asteroid belt in our solar system between Jupiter and Mars by getting caught up in Jupiter’s gravitational pull, but they can also be thrown out of the larger Kuiper Belt, located beyond Neptune towards Pluto, by Neptune’s gravity.
But what can we do if one was ever thrown our way? Would we have any chance of averting the disaster or will we always be prisoners to the will of the cosmos?
Luckily there are people watching the skies for this exact purpose at places such as the SpaceGuard center in the UK who focus on planetary defense and the impact threat. You may even be surprised to know that there are collision avoidance strategies being drawn up based on the ideas of deflecting or destroying Earth-bound asteroids that could be ready to be put into place should the need ever arise.
But what if we can’t stop it?

Deflecting asteroids is one thing but how do we avoid those pesky Neutron stars or any of the other monsters hiding out there in the dark? In about 5 billion years the sun will die. Having used up all its hydrogen fuel it will begin to expand in size as it swells into a red giant enveloping Mercury and Venus at first then eventually Earth and possibly Mars too. If the human race is still around in 5 billion years time we will definitely be needing to move on up and out by that time or face certain extinction. But how would we do this? Where would we go and how would we all get there are all questions that would need extensive studying in order for them to be answered to make such a thing possible. So, let’s have a look at them.

• Why Are We Going?

There could be any number of reasons why would we need to evacuate Earth so lets take a look at a few possibilities. Black holes have featured in many works of science fiction as agents of doom and terror, a force so powerful not even light can escape its pull even the name brings feelings of incomprehension and awe. Black holes form when any stellar object reaches a certain critical density and collapses in on itself to form a singularity, an area of space-time that is infinitely small while at the same time infinitely dense, thus distorting space-time into a vortex known as a black hole. The gravitational forces produced by black holes are what give them their immense power; should one ever cross the black hole’s event horizon (the area in which gravity becomes to strong for even light to escape) then a process called Spaghettification comes into play in which you would begin to get stretched like quantum spaghetti into the black hole due to the difference in strength between the forces acting upon you starting with your feet eventually consuming you entirely.

Should a black hole ever form in our solar system I highly doubt there would be much we could do as it may already be too late and we would have no chance to evacuate Earth. Another deep sky nightmare would be the previously mentioned neutron star. Formed by the gravitational collapse of a massive star during a supernova, neutron stars are made almost entirely of neutrons and have a density 500,000 times greater than that of the Earth, all packed into a sphere with a diameter no larger than Brooklyn, New York. The density of such an object is roughly the equivalent of the entire human population crushed down to the size of a sugar cube! Like any star, neutron stars are moving against a backdrop of other cosmic objects and can be detected and tracked here on Earth, So what if we did detect one that was heading straight for us? Would there be anything we could do to divert or destroy it? The short answer?

No.

We can predict how long it will take to reach us and how close it will need to get for its effects to start to be felt but once we know those things, then what? Lets say we’ve found one that will reach us in 100 years, that means the countdown has begun and we need to start thinking about the logistics of moving 7 billion people from one planet to another. There wont be time to double-check and triple check that the conditions are perfect on a rocket that has never been designed before using current technology with people who don’t have the best reputation for getting on. Well, good luck to any one who thinks they can make that happen.

• Where could we go?

At present we have a catalogue of about 9 different exo-planets believed to be habitable, with many more pending confirmation. This is good news for a species needing to find a new home, so what are our options? What kind of planet would suit us best? For intelligent life to survive an environment must be neither to hot nor to cold for liquid water to form on the surface. It must have a breathable atmosphere (Although this is debatable according to several theories in which humans could populate a planet in geodesic domes within which we could control our own atmosphere) and it must have a gravitational force similar to that of our own planet, after all what good is a planet on which we can barely move under the strength of its gravity?

The nearest potentially habitable new home to us is Gliese 581g orbiting the star Gliese 581. Detected via Doppler spectroscopy (Or “the wobble method”), its very existence is at the moment is still unproven, yet many astrophysicists are confident it could bear the conditions for supporting life. Just as the moon will only show one face to the Earth Gliese 581 g is predicted to be tidally locked to its star Gliese 581, meaning that one half would be perpetually covered in daylight and on the other half darkness.

From our current position here on Earth we would have to travel approximately 22 light years (or if my maths is correct 1.3 quadrillion miles) to get to Gliese 581g and, depending on the speed at which we travel this may take many generations. Whatever mode of transport we used would have to be able to travel at extremely high speeds for very long periods of time and be able to sustain the entire population of the planet for decades or even centuries. Such modes of transport have only ever existed in science fiction and even if it was possible to build it, how would you power such a massive craft?

•  How would we get there?

As we considered our options on transport we would instantly come up against a problem we could not likely solve. How do we get every single person on the planet, and presumably a few animals with them, off this planet and onto a new one? The answer would most likely be that we can’t. Interstellar transport on that scale is not within our realms of capability as a species just yet so we would have to face a harsh reality and accept that not everybody’s going. This in itself causes another problem: who the hell does get to go? Having accepted that, we would need to start thinking about how big we can feasibly build it. Maybe enough for 100 million people? 200 million max? That’s about 0.01% of the population…

The next problem is not only who gets to go but what kinds of people who be better suited to go and populate a different planet? What kind of genes would be best suited for space based reproduction?

Inuits, for example, would have the perfect genes for space reproduction as they have endured extremely harsh environments for thousands of years. Human development also relies heavily on the force of gravity: too little and your bones and muscles would wither without sufficient effort to keep them strong and healthy. On the opposite end of the scale to much and it is possible that newly born’s bones would distort and disfigure under the strain and muscles would not develop as they have evolved to on Earth.
As there is no gravity in space, we would need to create our own in order to ensure we survive space travel. Luckily for us there is one method of creating “artificial gravity” that we already know about. If, for example, we were to build our ship in the shape of a tube, we could harness centrifugal force to mimic gravity by rotating the tube during flight thus enabling ourselves to live under “normal” gravitational conditions.

But how would we get it going in the first place? What kind of fuel could we use to shoot something really big through space at massive speeds? Solar power would not produce enough energy for us to get to the speeds we would need to in order to get there in a reasonable amount of time.
The problem with chemical fuel systems such as those run on conventional rocket fuel is that you always need to bring more than you need in order to compensate for the extra weight of the last bit of fuel added and this is why it would never work. Anti-matter is another phenomena that has been studied for its potential as fuel but so far the idea of running something that destroys everything it touches through an engine has pulled up blanks. The other problem with anti-matter is the rate at which it can be produced for example, 250 grams of antimatter would take 2.5 billion years of the energy production of the entire Earth to produce.

In fact, the answer may have been under our noses for some time. The idea of using nuclear pulse-propulsion as a method of interstellar transport has been around since the 40’s and in 1958 Project Orion was the first attempt at designing a rocket that traveled using small directional nuclear devices exploding and absorbing the shock through a giant pusher plate attached to a spacecraft with shock absorbers. By the time the Partial test ban treaty shut the project down the US and Soviet Union had already detonated at least nine nuclear bombs (Including thermonuclear bombs) in space. Orion is one of very few interstellar space drives that could theoretically be constructed with presently available technology and could eventually be our last hope.

Speed will be critical in getting us there as quickly as is safe to do so, as the longer we are in flight, the more time there is for something to go wrong. Lets try some maths to work out how fast we’d need to go to get there in a reasonable amount of time. It has been estimated that the weight of the entire population of the planet is probably close to 576 million tonnes, this means we would need an awful lot of power to get things up to speed. Theoretically Nuclear pulse-propulsion has the potential for travel at around 6% the speed of light which is roughly 40 million miles per hour or nearly 18 thousand kilometres a second. The size of the ship would probably mean that we would have to build it in space if we ever wanted to get it going (the idea of detonating 3-6 nuclear devices at 6 second intervals on the surface of the planet is not a popular one) although even this we have experience in with things like the international space station. One of the problems with building in space is space junk. Thousands of pieces of debris from satellites, old rocket stages and such all orbiting around the Earth at high speed pose a threat to the construction (and constructors!) and makes building in space and extremely risky scenario for such an important mission. Nevertheless there is indeed hope.

We may one day come across a situation that forces us to leave this planet and become the first known experimenters in directed panspermia and fortunately for us we do posses technology now that would enable us to do it. We can only hope that as time goes on this technology will be improved upon and made more efficient so as to perhaps, in the event of a cataclysmic cosmic event, more lives could be saved and our journey into space safer. For now we can rest assured that there has been nothing so far that has forced us to test this theory.