What If An Asteroid Was Heading For Earth?

What If an Asteroid Was Heading for Earth?

The fear that an asteroid might crash into the Earth at any moment is as chilling as it is unfounded. Despite what Hollywood would have you believe, asteroids are not magnetically linked to Earth, and it’s unlikely that an asteroid the size of Texas will fix us in its sights any time soon. Yes, celestial objects and asteroids do enter our atmosphere all the time, and some in modern history, including the 1908 Tunguska event and the 2013 Chelyabinsk meteor, have caused significant damage. But asteroids like these are localized and do little to affect the world at large. A life-destroying, Earth-shattering asteroid hasn’t struck us for a good 66 million years, and one is unlikely to hit us in the near future.

But, if this WERE to happen, we’d probably have plenty of warning. As of 2018, the most likely candidate for a major collision in the near future is asteroid 2010 RF12, which has a 5% chance of making impact with Earth in September 2095. This asteroid is only seven meters in diameter and weighs 500 tonnes, making it look like a pebble next to the asteroid that wiped out the dinosaurs. Known as the Chicxulub impactor, that asteroid was 10-15 kilometres across and its impact was so great that it decimated the surrounding area and sent the Earth into an impact winter - resulting in the extinction of 75% of species on the planet. Today, this asteroid would be designated “extinction class”, which is NASA terminology for asteroids 10 kilometres or larger in diameter.

If an asteroid of this size were hurtling towards Earth, rest assured we’d see it coming long before it loomed above. The Torino scale, which categorizes the danger of near-Earth objects, accounts for potential impacts up to one hundred years from the present. There are cases where impact predictions have been even further down the line, such as 1950 DA, a one kilometre wide asteroid predicted to hit Earth in 2880. Meanwhile, the much smaller asteroids that reach Earth on a daily basis mostly burn up in our atmosphere.

While researchers are confident about the when, the where is a much more difficult affair, as it’s hard to predict an asteroid’s actual trajectory. Additionally, an asteroid that may have a 5% chance of impact two hundred years from today may have a 95% chance of impact one hundred and fifty years into the future. Luckily, we should still have enough time to prepare should an asteroid or comet drastically change course and present a more substantial threat. NASA’s Planetary Defense Coordination Office predicts that we could accurately assess an asteroid greater than 100-meters decades in advance. How many decades is unclear at this point, but NASA believes they’d be able to spot and plan for an asteroid strike well in advance of its potential impact.

Of course, the extent of our preparations would depend largely on the size of the asteroid. And believe it or not, NASA actually has various plans in place for defending Earth against rocky invaders.

Although it might seem like an obvious solution, shooting an asteroid out of the sky from Earth isn't one of them, for several reasons. For one, the asteroid would need to be so close that it would already be too late. Secondly, no such weapon exists. Asteroids are both incredibly heavy and incredibly fast, so it would be like trying to punch away an oncoming truck. Even if we COULD blow it apart, the resulting chunks and debris would still pose a risk.

NASA’s plans rely instead on deflection. The first method, designed to deal with asteroids up to 500 metres in diameter, is their ominous-sounding gravity tractor. Rather than some sort of sci-fi-derived graviton beam, the idea involves sending up a massive spacecraft to divert the asteroid using the craft’s own gravity. Over a years-long period, the spacecraft could enact enough of a gravitational pull on the asteroid to gradually steer it clear of Earth. While the gravity tractor is an untried, theoretical option, NASA’s confidence in detecting oncoming asteroids suggests they’d have plenty of time to iron out the kinks.

A second method of deflection is called kinetic impaction. A kinetic impactor is a high-speed spacecraft that would be intentionally hurled into an asteroid to deflect it off course. Fortunately, such a craft wouldn’t require a significant amount of time to build and launch. NASA states that if a dangerous asteroid were detected tomorrow, it would only take them around 20 years to build and launch one. Given enough time, NASA could even send a craft to the asteroid to study its composition and trajectory to allow for a more successful impact.

NASA is already hard at work on a kinetic impactor called the Double Asteroid Redirection Test (or DART), which is being managed by the Planetary Missions Program Office at Marshall Space Flight Center for NASA’s Defense Coordination Office. DART is planned to crash into the 150-meter long moonlet of asteroid Didymos at a speed of 6 km/s, which should be enough to change its trajectory by less than one percent. NASA will then study the asteroid’s course with land-based telescopes to observe DART’s success. Expected to launch sometime between December 2020 and May 2021, DART will make contact with Didymos in October 2022.

For bigger bodies, or with a shorter response time available, there’s the nuclear option aboard the hypothetical HAMMER - aka the Hyper-velocity Asteroid Mitigation Mission for Emergency Response. Another NASA design, this theoretical craft could either act as a kinetic impactor, or deflect asteroids using a nuclear explosion. A fleet of such probes could be sent up into the path of especially dangerous asteroids.

Unfortunately, the largest asteroids, measuring tens to hundreds of kilometres across, would present a challenge even for NASA’s kinetic impactors. NASA states that it might need many decades to build an impactor that could conceivably deflect an asteroid hundreds of kilometres in diameter.

Given enough time, it’s possible that all of Earth’s governments would pool funds into technological development and research. Maybe our impending doom would be enough to finally unite the world. If we discovered that a real monster asteroid was heading towards us, we would need to get a significant move on and develop some hitherto unforeseen technologies to knock it away.

As things stand today, in the unlikely scenario we DID somehow miss an extinction class asteroid about to hit us in the near future . . . well there’s really nothing we could do about it. NASA wouldn’t have enough time to develop a solution, and even if they did, there wouldn’t be enough time for it work. With no large-scale kinetic impactors built to date, it's possible we’d be herded into nuclear bunkers and forced to live out the rest of our lives – or at least the next few decades – underground. Places like Virginia’s Mount Weather Emergency Operations Center and Switzerland’s Sonnenberg Tunnel have been constructed to protect government officials and citizens from natural disasters. But when we emerged, we’d be faced with a totally different planet, as most of the species we know today would be extinct.

And if that TEXAS-sized asteroid suddenly came calling? Well, unfortunately there’d really be no hope. An asteroid that size would release billions of times the energy of our largest atomic bombs and wipe out all life on the planet. Worse still, there's a chance it might not be an instantaneous death for everyone. People far from the impact site might have to wait minutes before the spreading fireball reached them . . . and if they could somehow survive that, the seismic effects, air blast, and ejecta would do the rest.

But, hey at least you’d have time to make your peace with death.