Asteroid Strikes

Asteroid Impact Avoidance

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Introduction

In Earth’s 4.5 billion year history it has been struck by approximately 60 asteroids large enough to wipe out entire continents. In the 300,000 years that humans have inhabited Earth we have witnessed none of these. With millions of asteroids orbiting the Sun it is only a matter of time before history repeats itself. Should Earth be threatened by a life threatening asteroid impact, how will we handle it? Until recently the idea of preventing an asteroid from hitting Earth had seemed impossible. Throughout history human ingenuity and evolving technology has allowed us to achieve things previously thought impossible. So why should the same not be said about redirecting asteroids? A system involving the use of Gravity Tractors should be developed to mitigate the effects of asteroid strikes.

What Is An Asteroid?

Asteroids are often confused with comets or meteorites. It is important to note that they are not the same thing. An asteroid is a large chunk of rock consisting of clay, nickel-iron, and occasionally ice, orbiting the sun. They range from 10 metres to 500 kilometres in diameter. Comets and asteroids are usually the same size and contain similar material makeup, however, comets are made up of 15% frozen gases and water. This is why they appear to have long bright tails, caused by the sun rays reflecting off the melted ice as they fly through space. Comets also travel at a much faster rate than asteroids with the fastest ever recorded comet travelling at a speed of 600 kilometres per second compared to the fastest ever asteroid with a speed of 28 kilometres per second. A meteorite is the same as an asteroid, albeit a significantly smaller version. Asteroids smaller than 25 metres in diameter will usually burn up entirely on entry to the Earth’s atmosphere. The larger asteroids (around 100 metres before they burn up) that make it through the atmosphere and to the surface are dubbed meteorites. If an asteroid or comet is close to the Earth it is called a Near Earth Object (NEO). A NEO’s size is usually described by its diameter. This is because the only semi-accurate way to measure the actual mass of a NEO is to calculate the amount of light that is reflected off of its surface. Alan Gilmore explained this to us in greater detail during our interview with him.

Link to Interview with Near Earth Object Expert, Alan Gilmore.

What Are The Effects Of An Asteroid?

We know from history the destruction that asteroids can cause. 65 million years ago an asteroid, named Chicxulub, caused the mass extinction of nearly all life on earth. This event is known as the Cretaceous-Tertiary Extinction (K-T Extinction). It was one of the largest mass extinction events to ever occur in Earth’s history. It is estimated that 75% of life on Earth at the time was wiped out. The asteroid that wiped out the dinosaurs is one of most informative and recent examples of what would happen if an asteroid was to collide with Earth. One of the most important things to remember is that asteroids are like all other natural hazards, they come in different sizes. The size of the asteroid will determine the severity of its effect on Earth. An asteroid smaller than 25 metres will burn up on entry to the atmosphere while an asteroid with a diameter of 1 kilometre will cause, at worst, regional damage to an area. The asteroid that wiped out the dinosaurs had a diameter of 12 kilometres and caused a chain reaction all over the World. As Chicxulub struck just off the Coast of Mexico it caused earthquakes, tsunamis and wild fires over 70% of the Earth’s surface. It threw massive clouds of ocean spray and rock sediment into the air that covered the earth like a blanket. As the moisture and sediment drifted back down to the surface, it caused a rise in ocean acidity and temperatures that killed off many ocean species, limiting the supply of prey for larger ocean predators of the time. If an asteroid the size of Chicxulub hit Earth today it would have a severe impact on all of humankind. It would trigger 12.0 magnitude earthquakes all around the World. To put this in perspective, the biggest ever recorded earthquake (Chile, 1960) had a magnitude of 9.5 on the Richter scale. The tsunami caused by the asteroid impact would be a towering 1,500 metre high wall of water. This tsunami would sweep through countries and likely flatten entire cities weakened by the preceding earthquakes. All of these effects only further prove the need for a contingency plan if an asteroid were to head towards Earth.

Different Solutions

There are dozens of theoretical solutions to stop an asteroid colliding with Earth. However, a great percentage of these solutions are only theories and would need decades of research and development to be a viable option. One of these theories is an incredibly powerful laser, used for redirecting asteroids and NEO’s. It works by burning away one side of the asteroid, creating a natural thrust, changing the trajectory of the asteroid away from the Earth. Another theory involves attaching thrusters to the asteroid to change its trajectory and speed. These solutions could be a possible defensive option, but at the moment human technology is simply not yet advanced enough for these to be a reliable option. When dealing with NEO’s, timing is everything. If you were to utilise a defence measure 1 year before impact, even with the help of the measure, the asteroid could still hit the Earth. However, if you utilise the measure 5 years before impact the same change of trajectory will result in the asteroid passing Earth at a safe distance. This concept is explained in the picture linked below (please note that the images shown are not to scale). Three reliable and effective options include: Double Asteroid Redirection Test (DART), nuclear missiles, and a Gravity Tractor.

DART

DART is the world’s first attempt at utilising human technology against cosmic forces. DART is a small space craft with a single thruster for propulsion and monitoring equipment for observation of the asteroid. The satellite was launched on 24th November 2021 in partnership with SpaceX and NASA. It is now set on a predetermined collision course with a moonlet asteroid named Dimorphous. Dimorphous orbits it’s bigger twin asteroid named Didymos. The purpose of the mission is to demonstrate and understand how a kinetic impact from a satellite will affect an asteroid’s course. This will be demonstrated in September 2022. If this experiment proves successful, DART will most likely become earth's first line of defence against asteroids and NEO’s. The cost of DART is around 324 million New Zealand Dollars. This method is predicted to be the safest of the listed defensive measures with minimal repercussions for Earth.

Nuclear Missiles

You could describe nuclear missiles as a “last resort option”. Nuclear missiles are currently an emergency asteroid protection system for Earth and are safely researched and monitored by the National Aeronautics and Space Administration (NASA) and the National Nuclear Security Association (NNSA). It would take 4,000 nuclear bombs to destroy an average sized asteroid, and with each nuclear missile costing around 42,000,000 million New Zealand dollars, this comes to a total of 172,000,000,000 billion dollars. The reason that nuclear missiles are a last resort is because of the repercussions that come with using them. There are two methods to defend Earth from an asteroid using nuclear missiles. The first and safest is to explode a nuclear warhead near, but not on, an asteroid in an attempt to redirect it. The second is only to be used in extreme situations. The idea is to destroy the asteroid before it makes contact with the Earth. However the consequences of this method make it extremely unsafe. When an asteroid is blown up in this way the chunks and segments of the asteroid don’t just disappear. These highly dangerous fragments of mass destruction will rain down on earth in a radioactive meteor shower. The consequences of this method alone are enough to rule it out of most debates immediately.

Gravity Tractor

The Gravity Tractor is most likely to be the safest and most reliable solution. A Gravity Tractor is a spacecraft or satellite, similar in design to that of DART. The idea is to have the spacecraft drift along side the asteroid and use the gravitational pull created by the spacecraft to redirect the asteroid. Alan Gilmore, Retired Superintendent at Mount John Observatory at the University of Canterbury, has concluded that the Gravity Tractor is the most reliable and safest option for asteroid defence. Gravity Tractors can redirect asteroids away from Earth without making contact with the large rocky mass, making this the preferred option as there is a very small chance the asteroid would break apart while this is done. It is also the cheapest option at only 430 million dollars

The Final Conclusion

Asteroids are not likely to threaten us in the near future as all Near Earth objects and their path through our universe is closely monitored and none have been predicted to collide with Earth for the foreseeable future. Throughout this inquiry we have researched many ways to redirect an asteroid on a crash course with Earth. The majority of which are only ideas and theories that could not yet be achieved with the current technology available. The three solutions listed above are the best and only reliable solutions found by us in collaboration with experts in the field of Near Earth Objects. We have determined through emails back and forth between experts and studying the information at hand that the most effective and reliable solution will be the Gravity Tractor. The reason that we found the Gravity Tractor to be the foremost solution is the ability to use it multiple times and because of it being the most reliable of all the solutions found. At 430 million dollars the cost to build, launch and move an asteroid using a Gravity Tractor is cheaper than that of DART or a Nuclear Warhead. Writing this report we can conclude that everyone can sleep comfortably knowing that we have the means to protect Earth from an asteroid.

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