If you ask yourself what the biggest threat to human existence is you'd probably think of nuclear war, global warming or a large-scale pandemic disease.
But assuming we can overcome such challenges, are we really safe?
Living on our blue little planet seems safe until you are aware of what lurks in space.
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Researcher discusses 6 cosmic catastrophes that have the potential to wipe out the Earth. Daniel Brown explains that although some are deadly events, others would just cause other issues like loss of electricity and internet
1. High energy solar flare
Our sun is not as peaceful a star as one might initially think.
It creates strong magnetic fields that generate impressive sun spots, sometimes many times larger than Earth.
It also ejects a stream of particles and radiation – the solar wind.
If kept in check by Earth's magnetic field, this wind can cause beautiful northern and southern lights.
But when it becomes stronger, it can also influence radio communication or cause power outages.
The most powerful magnetic solar storm documented hit Earth in 1859.
The incident, called the Carrington Event, caused huge interference with rather small scale electronic equipment.
Such events must have happened several times in the past, too, with humans surviving.
If solar flares were to hit Earth there wouldn't be electricity, heating, air conditioning, GPS or internet – food and medicines would go bad
The truth is we would suffer greatly if we underestimate the dangers of a possible Carrington or even more powerful event.
Even though this would not wipe out humanity instantly, it would represent an immense challenge.
There would be no electricity, heating, air conditioning, GPS or internet – food and medicines would go bad.
2. Asteroid impact
We are now well aware of the dangers asteroids could pose to humanity – they are, after all, thought to have contributed to the extinction of the dinosaurs.
Recent research has made us aware of the large host of space rocks in our solar system that could pose danger.
REDIRECT MISSION COULD SAVE EARTH FROM AN ASTEROID
In Ion Beam Deflection, the plumes from the thrusters would be directed towards the asteroid to gently push on its surface over a wide area. A thruster firing in the opposite direction would be needed to keep the spacecraft at a constant distance from the asteroid.
The Ion Beam Deflection approach is independent of the size of the asteroid, and it could be demonstrated on either mission option.
In the Enhanced Gravity Tractor approach, the spacecraft would first pick up a boulder from the asteroid's surface as in mission Option B.
The spacecraft with the collected boulder would then orbit in a circular halo around the asteroid's velocity vector.
The mass of the boulder coupled with the mass of the spacecraft would increase the gravitational attraction between the spacecraft and the asteroid.
By flying the spacecraft in close formation with the asteroid for several months the very small gravitational forces would produce a measurable change in the asteroid's trajectory.
A kinetic impactor could also be launched as a secondary payload with the spacecraft or on a separate launch vehicle, and it would collide with the target asteroid at high velocity while the spacecraft observed the impact.
We are at the starting point of envisaging and developing systems for protecting us against some of the smaller asteroids that could strike us.
But against the bigger and rarer ones we are quite helpless.
While they would not always destroy Earth or even make it uninhabitable, they could wipe out humanity by causing enormous tsunamis, fires and other natural disasters.
3. Expanding sun
Where the previous cosmic dangers occur at the roll of a dice with a given probability, we know for certain that our sun will end its life in 7.72 billion years.
At this point, it will throw off its outer atmosphere to form a planetary nebula, ending up as a stellar remnant know as a 'white dwarf'.
THE SUN IS EXPANDING
Five billion years from now, the sun will have grown into a red giant star, more than a hundred times larger than its current size.
While this metamorphosis into the giant star will change the solar system, scientists are unsure what will happen to the third rock from the sun.
We already know that our sun will be bigger and brighter, so that it will probably destroy any form of life on our planet.
But whether the Earth's rocky core will survive is uncertain.
At the end of its evolution, seven billion years from now, the sun will become a tiny white dwarf star.
As the sun becomes older, it will become cooler and larger. As a result, in about 7.59 billion years, our planet will spiral into the outer layers of the hugely expanded dying star and melt away forever
But humanity will not experience these final stages.
As the sun becomes older, it will become cooler and larger.
By the time it becomes a stellar giant it will be big enough to engulf both Mercury and Venus.
Earth might seem safe at this point, but the sun will also create an extremely strong solar wind that will slow down the Earth.
As a result, in about 7.59 billion years, our planet will spiral into the outer layers of the hugely expanded dying star and melt away forever.
4. Local gamma ray burst
Extremely powerful outbursts of energy called gamma ray bursts can be caused by binary star systems (two stars orbiting a common centre) and supernovas (exploding stars).
Radiation from a gamma ray could damage and destroy our ozone layer, leaving life vulnerable to the sun's harsh UV radiation
These energy bursts are extremely powerful because they focus their energy into a narrow beam lasting no longer than seconds or minutes.
The resulting radiation from one could damage and destroy our ozone layer, leaving life vulnerable to the sun's harsh UV radiation.
HOW GAMMA RAYS CAN KILL US
On Earth we are shielded from most gamma rays in space by our ozone. But gamma-ray bursts, on the other hand, are much more powerful.
A gamma ray burst is the equivalent of taking all the stars within a hundred million light years and focusing it into one kind of energetic 'laser beam'.
But even a more distant GRB could still end life on Earth and it wouldn't need to score a head-shot to kill us.
If originating from a few thousand light years away, it would be a hundred light years wide by the time it reaches us, washing over the solar system like a tidal wave.
Our ozone would not be strong enough to protect us in this case.
Because gamma rays travel at the speed of light, we would have no warning of the attack until it hit us. By that point it would be too late, and most complex life on Earth would be dead.
Astronomers have discovered a star system – WR 104 – that could host such an event.
WR 104 is about 5,200-7,500 light years away, which is not far enough to be safe. And we can only guess when the burst will happen.
Luckily, there is the possibility that the beam could miss us entirely when it does.
5. Nearby supernovas
Supernova explosions, which take place when a star has reached the end of its life, occur on average once or twice every 100 years in our Milky Way.
They are more likely to occur closer to the dense centre of the Milky Way and we are about two-thirds of the way from the middle – not too bad.
So can we expect a nearby supernova anytime soon?
Astronomers have estimated that a supernova would need to be within at least 50 light years of us for its radiation to damage our ozone layer. So it seems this particular star shouldn't be too much of a concern. Picture is 70,000 light-years
The star Betelgeuse – a red super giant nearing the end of its life – in the constellation of Orion is just 460-650 light years away.
It could become a supernova now or in the next million years.
Luckily, astronomers have estimated that a supernova would need to be within at least 50 light years of us for its radiation to damage our ozone layer.
So it seems this particular star shouldn't be too much of a concern.
6. Moving stars
Meanwhile, a wandering star on its path through the Milky Way might come so close to our sun that it would interact with the rocky 'Oort cloud' at the edge of the solar system, which is the source of our comets.
This might lead to an increased chance of a huge comet hurtling to Earth.
Another roll of the dice.
The sun itself follows a path through the Milky Way that takes us through more or less dense patches of interstellar gas.
A wandering star on its path through the Milky Way (pictured) might come so close to our sun that it would interact with the rocky 'Oort cloud' at the edge of the solar system, which is the source of our comets. This might lead to an increased chance of a huge comet hurtling to Earth
Currently we are within a less dense bubble created by a supernova.
The sun's wind and solar magnetic field help create a bubble-like region surrounding our solar system – the heliosphere – which shields us from interacting with the interstellar medium.
When we leave this region in 20,000 to 50,000 years (depending on current observations and models), our heliosphere could be less effective, exposing Earth. We would possibly encounter increased climate change making life more challenging for humanity – if not impossible.
The end of humanity on Earth is a given.
But this is not something to make us crawl under a table.
It is something that we cannot change, similar to our lives having a definite start and end.
This is what defines us and makes us realise that the only thing we can do is make the most of our time on Earth.
Especially when we know that Earth needs a careful balance to sustain humanity.
All the above scenarios harbour possible destruction, but in every instance they also offer beauty and wonder.
In many cases, they produce what allowed us to be created.
So rather than looking into the night sky and wondering what will kill us next, we should marvel at the depth of space, the wonders therein and the sublime nature of the universe.
Be inspired by space. It offers future and meaning.
Daniel Brown, Lecturer in Astronomy, Nottingham Trent University
This article was originally published on The Conversation. Read the original article.
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