MIT researchers devised a step-by-step plan to help scientists make the right decisions in time to prevent a potentially catastrophic collision.

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In order to effectively deflect a potentially dangerous asteroid several characteristics such as mass, surface composition, and trajectory need to be known - Image Credits: Christine Daniloff, MIT

Researchers from the Massachusetts Institute of Technology (MIT) devised a step-by-step plan to help scientists make the right decisions in time to prevent a potentially catastrophic collision. Their findings will be published in the science journal: Acta Astronautica

It is not entirely inconceivable that a giant space rock will collide with our planet in the future. Our solar system contains a lot of asteroids flying around. It is quite possible that every now and then, one will head on a trajectory towards Earth.

As a matter of fact, it is expected that on April 13, 2029, an icy piece of space rock known as 99942 Apophis, bigger than the Paris Eiffel Tower, will whizz by Earth with a speed of approximately 2200 miles per hour (30 km per second), grazing the planet’s sphere of geostationary satellites.

Apophis

Apophis is named after the Egyptian god of chaos. That name seems aptly chosen as it is hard to pinpoint its trajectory. Previous observations suggested that the beforementioned flyby would take the asteroid through a so-called 'gravitational keyhole', altering its path so that on its next flyby, it would crash into Earth with potentially disastrous consequences. Fortunately, later observations showed that it would likely miss our planet.

Apophis is not the only space rock that could come dangerously close to the Earth. Asteroid Bennu might as well shave closely past Earth in the future. Therefore it is never early enough to devise some clever plans in case a planetoid is once again on a collision course with our planet.

Scientists from MIT have developed a framework to help decide what type of mission would be most effective in diverting an inbound asteroid. The framework takes into consideration an asteroid’s momentum and mass, its proximity to a gravitational keyhole, and how long scientists will have before the collision takes place. All of these factors contain different degrees of uncertainty. These degrees of uncertainty have to be taken into consideration as well in order to identify the best way to mitigate a potential impact.

Sung Wook Peak, the lead author of the study, stated in an interview that we have mainly considered last-minute diversion plans. These plans are aimed at the asteroid when it is already headed in the direction of Earth after it has passed through a crucial gravitational keyhole. Peak is involved in the idea of preventing keyhole passage well before Earth impact. Het calls it similar to a 'preemptive strike, with less mess.'

This image shows the distance between the Apophis asteroid and Earth at the time of the asteroid’s closest approach. The blue dots represent satellites orbiting Earth and the pink line represents the ISS - Credit: Marina Brozović/NASA/JPL -

Previous planet-killer deflection strategies

Fourteen years ago, NASA scientists concluded that in the event of an impending asteroid collision, the most productive way of deflecting would be by launching a nuclear missile into space. The force generated by its detonation would blow the asteroid away. A nasty consequence of this strategy would be that the Earth would then have to deal with potential nuclear fallout. Understandably atomic weapons in space are a very controversial topic.

The next best alternative would be to send up a rocket, spacecraft some other sort of projectile that, if pointed at just the right direction, with sufficient velocity, should collide with the asteroid transferring some portion of its momentum, and bend it off its path towards Earth. Such a projectile is called a 'kinetic impactor'. Peak called the underlying physics to be sort of like playing billiards. The problem with this approach is that the properties of the asteroid, such as its momentum, and surface structure, must be known as accurately as feasible, which means that in planning a deflection mission uncertainty needs to be taken into account.

Professor Olivier de Weck, one of the co-authors of the study, mentioned that it certainly matters if the chance of success 99.9 percent or just 90 percent. Consequently, we have to be more clever in designing missions as a function of the level of uncertainty. According to de Weck, no one has studied the problem in this way before.

Three new strategies

The research team created a simulation code to identify the type of asteroid deflection mission that would have the best possibility of success, given an asteroid’s set of uncertain characteristics.

In essence, there are three different possible strategies in the case of an incoming asteroid. The ideal scenario is one where there is enough time to send two scouts: one to take essential measurements and the second to push the asteroid slightly out of its orbit before a larger projectile is launched that ultimately prevents a collision with Earth.

If there aren't enough resources or if there isn't enough time for the ideal scenario, we could go for sending just a single explorer to do measurements on the asteroid. If its essential properties are assessed, a targeted projectile will be launched to prevent a collision with the Earth.

When there isn't enough time for the second-best option, one last option would be to fire a projectile without forwarding 'reconnaissance' and aim to bounce the asteroid from its orbit by using kinetic energy.

Logically, the further away from Earth an asteroid is, the easier it gets to deflect it. Nudging it only a tiny bit from its course can make a huge difference over vast distances. The researchers fed particular variables such as the asteroid’s momentum, mass, and trajectory into the simulation in addition to the range of uncertainty connected with each of these variables. The most important variable of all is an asteroid’s proximity to a gravitational keyhole, as well as how much time scientists will have before an asteroid passes through that keyhole.

Image Credit: RomoloTavani via iStock - HDR tune by Universal-Sci

Testing the strategies

To test their strategies, the researchers carried out simulations on Bennu and Apophis. They simulated different distances and calculated at what range the relevant asteroids could best be averted. The team then examined which of the three previously mentioned strategies would best suit the particular case.

For instance, in the case of Apophis, tests show that if it takes five years or more for the asteroid to fly past Earth, it would be most effective to go for the plan with the two scouts. One to measure all the vital characteristics of the asteroid and one to nudge it out of collision course.

If we only have between two and five years before a space rock will pass through a gravitational keyhole, there may only be time just to send one explorer to measure things up after which a gravitational impacter will be launched.

According to Peak, we are in big trouble if Apophis will buzz by the Earth within one year. He stated that even a large collision body might not be able to reach the asteroid in time by then. This also applies to Bennu, be it that we already have some information about its composition, meaning that projectiles could be fired without sending a preliminary explorer.

The researchers' new tools will be useful in calculating the potential success of deflection mission in the future. Rather than changing the size of a gravitational impactor, experts might be able to alter the number of launches and send up several tinier spacecraft. Peak mentioned that we might also be able to use satellites that are no longer in use as kinetic impactors. Ultimately, if the necessary resources are available, we could launch projectiles from our moon as a more efficient line of defense.

All things considered, we can all go to bed worrying a tiny bit less about our potential impending doom from space if we decide to invest adequate resources and time into carefully planning our planetary defense.

Sources and further reading: MIT news release