Imagine a day, any day, where you’re going about your daily routine, going everywhere you’d normally go; except, on this random day, a NEO (Near Earth Object) has a trajectory that happened to line up cosmically with the Earth, and is close. While you’re in class, a shockwave strong enough to flatten the building and every other building for hundreds of miles around hits and you die, not knowing it was happening for more than a few minutes at most.
This is what scientists are trying to prevent when they set out to research asteroid impact avoidance. Humanity doesn’t want to end up like the dinosaurs. Though with this goal comes difficulty. There are a lot of different factors that play into an NEO’s trajectory: things like object size and mass, velocity, or even movement of thermal energy, in the case of the Yorkvosky effect. To predict the likelihood of an NEO impacting with our planet, scientists use telescopes with a wide-angle lens to identify objects that meet the classifications. They will also use software to assist in picking out these NEO’s from the image data. Luckily, the larger the asteroid, the more it is visible from Earth; Astronomers can detect the objects that pose a greater threat, sooner. However, this poses a dangerous dichotomy, as smaller objects can get much closer to earth without being detected until mere days before impact. This issue has become the focus of efforts to improve the world’s NEO prediction capabilities, due to it leading to the most destruction. Most proposed solutions involve simply establishing more satellites both on Earth and in orbit, but some have proposed satellites orbiting closer to the Sun to give them a wider angle of earth without much of the glare that Earth-based satellites struggle with.
There are a number of methods devised by astronomers and other scientists to deflect NEO’s that have an orbit on-track to collide with earth. One of the most developed of these is using a nuclear explosive device to either split a NEO into smaller parts (disrupting its orbit), or to propel the object off course by using the explosive vaporization of nearby matter as “fuel,” creating an effect similar to a rocket engine. This theoretical method is popular because nuclear explosives contain the highest energy concentration of all energy sources able to be utilized by humanity, and are relatively easy to deploy. The energy required to match the output of 1 Mt from a 0.5 ton nuclear payload by a standard kinetic impact would be unreachable. Some problems are posed by this solution though, such as the danger of newly radioactive asteroid debris raining down into earth’s atmosphere, if the potential trajectory is not extensively calculated.
Further methods of payload delivery have been developed, such as a dedicated satellite that would carry the nuclear payload, as well as a kinetic impactor device. This device would create an initial crater on the surface of the asteroid in which the device would be planted, in order to increase the efficacy of the detonation.
Object collisions happen naturally in space, and can transfer huge amounts of energy when they do. This can be imitated with man-made objects, designed to collide with NEO’s at a specified angle and velocity to knock them off of a collision course with Earth. This was demonstrated in NASA’s Deep Impact DART probe mission, wherein an unmanned satellite deployed an inert, solid copper impactor weighing 372 kg yet generated a force equivalent to 4.8 tonnes of TNT upon impact at 10.2 km/s. The mission was to discover what was in the center of the comet and not to offset its orbit, but it proved a good demonstration. The kinetic impact method harnesses the immense speeds achievable in orbit to turn relatively inexpensive metal into an incredibly powerful deterrent.
Out of all of the methods discussed, the method of focusing solar energy is likely the most far-fetched, but is theorized to be effective in certain scenarios. A satellite that functions as a giant mirror would be deployed near the NEO, focusing sunlight into a point on the surface. This point would undergo an effect similar to the initial effects of the nuclear detonation method, where solid material is vaporized to create thrust, propelling the NEO away from Earth. Sizes of the reflectors required would vary depending on the size of the NEO and the amount of warning given, but range from half the diameter to roughly equal to it. Unlike its alternatives, this method would function over a span of time, as opposed to an instantaneous point of impact or explosion. This would mean that more lead time would be required than simply the time taken to deploy the satellite; the time would vary based on the size of the NEO and its speed.
When dealing with the ability of mankind to control the behavior of celestial bodies, a conversation of ethics is needed, as actions taken could potentially spell doom for Earth itself. Any method created by humans could potentially be taken control of and abused by a nefarious political actor, granting a power similar to, if not greater than, nuclear armament. Even barring extremist takeovers, the question of who should be in control of these tools is a complicated one, especially taking into account actions that may affect certain nations more adversely than others.
Climate change is the largest threat facing life on our planet currently, but the threat of colliding NEO’s is that they could be granted that title at any time. It’s comforting to us that we have strategies to detect these objects quickly, and to potentially defend from them should they pose a danger to us. Starting in the 90s, astronomers started taking the topic seriously enough to fund significant research into planetary defense and Spaceguard, where further research continues. As global politics increase in complexity with each passing year, seeing an international debate on who should have the power to pilot a moon-sized solar powered orbital laser might not be far-fetched. Until then, the scientific community will hopefully strive for a solution that is economically and physically feasible, and that doesn’t give undue power to any group over another.
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"the scientific community will hopefully strive for a solution"-- If only we could count on the larger extra-scientific community to do the same. The ethical conversation has to include everyone, including the ethically-challenged community of elected politicians, if it is to have a chance of success.
ReplyDeleteThose links needed to be embedded in the text, not listed at the end.