Imagine a day when an asteroid over a kilometer in diameter, much like the one that is believed to have wiped out the dinosaurs, is detected and predicted to impact our planet. If this object were not properly controlled, it could lead to global catastrophe with billions of casualties (OECD 3). An impact could lead to the destruction of entire regions and populations through tidal waves, the partial blocking of sunlight, and firestorms of heated debris. With all the current technology, do we stand a chance of surviving a so called “planet-killer” asteroid?
Near Earth Objects (NEOs) are celestial bodies such as comets, asteroids, and small planets (excluding dwarf planets) whose orbital paths reach less than 1.3 astronomical units away from the sun. The probability of a NEO collision with the Earth is low; NEOs with diameters over 100 metres are expected to hit the Earth with an average interval of 10 000 years. Currently, there are very few NEO deflection methods being discussed, and most are not developed enough to propel a large NEO away from its predicted trajectory.
One potential deflection technique, called blast deflection, consists of using nuclear explosives to change a NEO’s velocity, and consequently, its trajectory. Nuclear fusion weapons would be set off above the Earth’s surface to change the object’s velocity while avoiding fracturing the object (as multiple pieces would hit the Earth, creating an even larger problem). Even a minor velocity change in the NEO’s motion could lead to the asteroid’s trajectory missing the Earth entirely, over the course of several years. Thus far, blast deflection may be the only viable strategy for the deflection of “planet killer” NEOs over a kilometer in diameter. However, many countries and organisations advocate for the abolishment of nuclear weapons, and very few countries possess nuclear weapons. Nuclear explosives also pose a major threat to the environment and the health of organisms, and are technically banned from use in outer space. This is why it is essential that alternative deflection methods are developed.
In 2011, a NASA team established the Solar Sail Demonstrator, a “Technology Demonstration Mission” intended to prove the versatility of a lightweight sail approximately 13,000 square feet in length that relies on the pressure of solar light to propel itself. A deflection method that has been considered is to place large solar sails on a small NEO so that the sunlight’s pressure could redirect the object away from Earth’s path. Unfortunately, the Solar Sail Demonstrator project was concluded before flight testing, and propulsion by solar sails is still only in experimental phases.
Another non-nuclear related deflection method is to use a “gravity tractor” device to divert the NEO from its original path. The device would have to fly alongside the NEO for many years to pull it out of its predicted trajectory, and therefore the approaching object would have to be detected early enough. Gravity tractors are easy to control and could most likely mitigate NEOs of any shape or material; however, they may not be an option for objects over 500 metres in diameter. Moreover, this technique has never been attempted, and many decades would be required to develop it.
Lastly, kinetic impactors are high-speed spacecraft that would crash into an NEO to alter its trajectory. NASA has tested kinetic impaction on a small scale with its 2005 Deep Impact mission, and the ESA is currently undergoing the Asteroid Impact Mission to develop a kinetic impactor. Once kinetic impactors are available, the National Academy of Sciences would require at least one to two years of warning time to deflect smaller NEOs, and at least a few decades for “planet killer” NEOs. Even then, kinetic impactors may not be able to change the orbit of the very largest objects.
The issue of Near Earth Objects is widely overlooked, even though it could have a detrimental effect on our society. As recent as February 15, 2013, a NEO entered the atmosphere and disintegrated above Chelyabinsk, Russia. Peter Brown at the University of Western Ontario, Canada concluded, from low-frequency sound waves detected by a global network, that the object had a diameter of around 17 metres and a mass of approximately 7000–10 000 tonnes when it hit the atmosphere. It caused a shockwave that “shattered glass and injured about 1,200 people” (Howell). It is of utmost importance for the world’s space agencies and governments to develop NEO deflection methods, and prevent another catastrophic impact.
Written by Maia Poon
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