Space is a pretty dangerous place, not just because of the endless vacuum or possible threat of annihilation from some alien race intent on harvesting our planet or whatever, but debris. Space debris in the form of asteroids specifically, these space rocks have the potential to cause incredible amounts of damage to anything the impact, so how do we defend ourselves from them? What’s the plan to protect our home planet from disaster? Ian Cornelli took the stage at New Scientist Live to talk us through some of the planetary defense procedures.

When our solar system first formed the outer planets actually moved closer to the Sun, over time however they began moving away to the orbits they now have. This shuffling back and forth left behind some huge asteroid belts thanks to the gravitational shenanigans. These giant bands of space rubble are constantly orbiting the sun in a chaotic but fairly predictable manner, which is great when it comes to forecasting possible dangers.

When it comes to defending the Earth there is a silent and unsung hero that has protected us from innumerable asteroid impacts; Jupiter. Jupiter is more than just a big ol’ ball of rock with a zit, it’s been watching our backs for thousands of years and it’s monumental size and gravitational field has pulled in countless objects. These objects could have had devastating effects had they reached Earth, instead they were pulled down to impact “harmlessly” onto Jupiter’s surface and save us from any number of disasters. So thanks Jupiter, we owe you many!

The Shoemaker-Levy comet strike is one of the most notable and observed impacts, where the gravitational forces exerted by Jupiter tore the comet apart. Fragments from the object were up to 2km in diameter and impacted the surface roughly 2 years later at approximately 60km/s. This kind of collision could have potentially leveled Earth and reduced it to an ash-covered ruin in an extinction level event. The impact scars from the collisions were more easily observed than that of Jupiter’s Big Red Spot and remained so for many months before the extreme weather took its toll.

So again, thanks, Jupiter! We would certainly not be here if it was not for that giant planetary body watching our arses! Of course this isn’t us actually doing anything and more of a luck of the draw, Jupiter happening to be in the right place to take one for the team is great and all but not foolproof, so naturally, we’ve come up with a collection of different methods for defending our precious Terra.

Asteroids and their impacts have different classifications, the most dangerous of all is the “Extinction Level”, as the name suggests these are objects that would either eradicate life on Earth immediately or create such an inhospitable environment that nothing could survive for long. Luckily these events seem to only occur every 10,000,000 years, like the one that is responsible for killing the dinosaurs and fundamentally altering the composition of Earth’s atmosphere. Smaller scale impacts occur far more regularly but have far smaller consequences.

For example, there is the Chelyabinsk Event from 2013 in Siberia. On February 15th an object measuring approximately 20m in diameter entered Earth’s atmosphere at an estimated speed of 19km/s, due to the angle of entry the object exploded in the air above Chelyabinsk Oblast, Russia. The object detonated with a force between 26-33 times that of the atomic bomb used on Hiroshima, the resulting blast wave shattered glass, caused structural damage to over 6,000 buildings and resulted in 1,491 reported injuries, two of which were serious but not fatal. Moments prior to the explosion the meteorite glowed more brilliantly than the sun and was visible for up to 62 miles away.

The damage caused by this impact was largely superficial, but it is the only known event of its kind to result in human injury. This impact could have had far graver consequences had the angle of entry into the atmosphere been steeper and the object actually making landfall. The Chelyabinsk meteorite is considered to be within one of the smallest size categories but the numbers show just how devastating an effect it could have had if it had impacted. It’s clear to see that some form of planetary defense system is necessary, considering this interstellar pebble nearly leveled an entire city.

When it comes to dealing with asteroids, size matters; The larger the object, the easier it is for our boffins to detect and determine its orbit. Of course, these larger objects present the largest threat in the sense that the bigger they are the harder they hit and the deader we become. Objects smaller than 150m in diameter represent a huge problem as they are the most difficult to detect accurately. Having seen the damage a 20m asteroid can cause without even touching the ground, there’s quite a big gap we should be concerned about. It’s not all doom and gloom though, the brain boxes keeping an eye on these overgrown space pebbles believe we should have nothing to fear for at least a couple of decades.

So just what methods of protection do we have? Currently, none, but there are a whole host of different ideas in the pipeline! Unsurprisingly explosive solutions are being evaluated for their feasibility, probably the use of a missile strike rather than landing a drilling crew on the surface of the asteroid and getting them to nuke it. Not that isn’t a totally valid method of doing it, just completely ridiculous.

Seriously, just teach the astronauts to drill…

The Gravity Tractor method is one that sounds most interesting but requires a substantial amount of time in order to prove effective. The idea is to send a space vehicle of some description to either hover or orbit close to the asteroid, once in place it would consistently thrust in a specified direction utilizing the craft’s gravitational force to manipulate the trajectory of the asteroid. This method would probably prove to be the most sustainable as in theory the object and the space craft should never come into contact. Once the adjustment has been made the vehicle could return to Earth for refueling and then be reused.

Kinetic Impact looks to be the most promising of the proposed methods for dealing with dangerous Earth-bound objects. Kinetic impact as the name suggests involves colliding two bodies to alter the trajectory of the risk object. Obtaining and directing a body of sufficient mass to accurately redirect such objects may be a challenge, however, the response time from detection to impact is estimated to be around 2 years, blindingly fast for a launch plan!

A Kinetic Impact test mission is scheduled to take place in Oct 2022. The Didymos asteroid has been detected and actually consists of two independent bodies, Didymos A and Didymos B (known as Didymoon). Didymoon orbits it’s brother, Didymos A, creating the perfect trial environment for testing the Kinetic Impact technique. The plan is to collide Didymoon with its brother in order to alter the latter’s trajectory. Cubesats will be placed to monitor the impact and relay information back to control. What is most surprising and quite promising is the cost per mission, estimated at roughly £250 million per launch which equates to £3.75 per UK citizen or €0.49 per EU citizen. A small price to pay to defend the Earth!

The final method worth mentioning is my favorite idea, despite it probably being the least effective; Solar Deflection, via Solar Sails or quite literally painting an asteroid. Solar Sail Deflection is the more technical method and the theory behind it is pretty interesting but also kinda nuts. The theory is thus, solar radiation warms the surface of the asteroid which is re-emitted from the asteroid’s sun facing side and generating a minor amount of thrust. This small amount of thrust does not effect small objects due to the tiny amount of thrust generated, nor does it influence larger asteroids as they are too heavy. Objects that fit within the mass-goldilocks zone, however, are a prime target for Solar Deflection.

Solar Deflection candidates are shielded from Solar Radiation either by Solar Sails, spacecraft that project a sunshade to block the light or by painting the surface of the asteroid a color that is more reflective to Solar Radiation and therefore preventing the asteroid from absorbing the energy in the first place. The Solar Sail method would also utilize a Gravity Tractor effect as well, combining both to be twice as effective, however, neither technique looks to be the best method for defending the Earth from bombardment.

Of course, these plans all mean nothing if we aren’t able to accurately detect and forecast the movements of this risky space rubble. There is a staff of 10 people working round the clock simulations in order to identify any possible hazards and allow us enough time to appropriately deal with the situation. Current models are looking up to 100 years in advance and are being constantly updated as new objects are discovered. Less reassuringly though is the fact that 9 out of 10 large objects remain unidentified and close calls of all kinds happen all the time… Let’s not dwell on that.

On a more positive note, there have been advances in telescope technology, creating a compound lens that is able to help detect smaller objects more easily. As mentioned above, these smaller objects appear to pose more of a threat to humanity due to the fact they move so quickly and are so challenging to identify. Advancements such as these may prove to be the best hope humanity has at avoiding another Armageddon style disaster movie.

Off-world manufacturing has been identified as an instrumental step in the defense of the planet. Utilizing a specially made 3D printer capable of turning the Lunar soil into a usable material would be the first step in establishing a sustainable habitat on the moon. From there it would be converted to a fuel production site that could be used to refuel and launch deep-space capable craft at a fraction of the cost of launches from Earth. I’d recommend reading Artemis by Andy Weir to get an idea of just how this would work, hell given how well he researches his novels you could probably use it as a case study.

So, the outlook is kind of bleak? We could be wiped out at any given moment by an inter-planetary body we never saw coming and we’d be powerless to stop it even if we did spot it, but the current forecast says that it’s unlikely to happen for at least a couple decades. Technologies are being advanced and plans are being put in place to stop any long-range threats we are able to detect in time and therefore we might just be able to protect ourselves from an extinction level event.

Honestly, it’s not the most inspiring of topics for conversation, but it certainly is fascinating to study… you just have to look past the existential dread.

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