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Should We Fear Asteroids? There Are An Awful Lot Up There… And One Might Be Heading Right For Us.

There may be very large reason that Dinosaurs aren’t around. A giant ball of rock, metal and fire hurtling at thousands of miles an hour into the Earth. But that’s ancient history right? Well, maybe not. Asteroids are more common that you think. And if you keep an eye on the news, we might be in for a close call relatively soon. But just how big is the risk? And what can we do about it?

Warning: Giant Rocks ahead.

A Galactic Swarm of Killer Asteroids

The undiscover’d country from whose bourn, No traveller returns, puzzles the will,
And makes us rather bear those ills we have, Than fly to others that we know not of? – William Shakespeare, Hamlet.

In a popular lecture, Astrophysicist Neil DeGrasse Tyson jokes about his new name for ‘Near Earth Objects’. These ‘objects’ are giant rocks within our solar system or have an orbital path crossing it. Neil suggests something a little less technical, ‘Killer Asteroids’. And he isn’t wrong. Although most small rocks burn up in our atmosphere, the big ones are a real problem.

Current estimates suggest that there at least 150 million rocks  greater than 100m wide flying around our solar system. That number doesn’t even consider what is hurtling inward from deep space. Although most are unlikely a threat, we don’t get much notice when one decides to visit. But where do they come from, and how can we predict their journeys?

An Asteroids Home

‘Knowing it and seeing it are two different things’ Suzanne Collins, Mockingjay

Its easy to classify the home of an asteroid. You can say ‘comes from within our solar system’ or ‘comes from outside of it’. Within our solar system there is one large asteroid belt between Mars and Jupiter, likely formed of debris left over from the formation of the planets. At the edge of our system there is the Kuiper Belt, (or more accurately orb), a tremendous interstellar cloud of icy rocks.

Most of the asteroids we encounter come from these two sources, but rarely something can be hurtled our direction from far away. These ‘Deep Space‘ asteroids are the true travellers, often traversing billions of miles of deep space. They may come from a colossal rock reservoir called the Oort Cloud, although we haven’t directly observed it yet.

So what guides these things? Do they have it in for us?

Gravity’s Missiles

“Sometimes I think gravity may be death in disguise. Other times I think gravity is love, which is why love’s only demand is that we fall.” – Shaun David Hutchinson

Asteroids, like the planets, orbit based on the principles of Gravity. Gravity is inversely powerful with distance (i.e it gets weaker the further you go,) but also grows with size. Things are said to ‘have gravity’, although the force itself is not quite understood. Nonetheless we understand its effect in space. Objects will ‘orbit’ around larger ones, at a path and speed dependent on their initial velocity and the gravity of other objects around it.

Stable orbits (like ours around the Sun,) differ from those orbits of many objects ‘caught’  by gravity. ‘Long Period Comets‘ for example have highly elliptical orbits, flying far into space before returning. When a large object passes causes a gravitational flux, things can fly off course. For us, that means the occasional flurry of Asteroids from the Kuiper Belt or beyond.

So, is one coming for us? And what can do about it?

Yes, There Is.

Dan, we didn’t see this thing coming? Well, our object Collison budget’s a million dollars, that allows us to track about 3% of the sky, and beg’n your pardon sir, but it’s a big-ass sky. – Armageddon 

In 2004 Astronomers made a startling discover. A huge asteroid named Apophis seemed scarily likely to hit us. But after modelling its trajectory after a 2014 flyby, it seems its chances to hit us will diminish in future (first in 2029, then 2036.) What worried us the most was not that it exists, but that it was spotted so late.

We can only watch a tiny percent of the sky at a time, and we miss things a lot. Chances are that you knew nothing of 2004 BL86, a mountain sized asteroid that passed us by in 2015. In fact, NASA warns us that if a ‘Doomsday’ asteroid were to appear, we would have ‘zero warning’.  Our first sign would be a flash of light, quickly followed by death.  However, if we did spot one by chance, we would have decades notice.

And in the cold reaches of space, there are a lot of candidates.

So what can we do? Short of spending huge amounts of time watching the sky, can we blow them up like in Armageddon? Well actually Yes. NASA have actually begun the design of a spacecraft to deliver nuclear warheads. The target is Bennu, an asteroid with a 1/2700 chance of hitting us in 2135. Short of that, other plans could include using gravity to nudge an asteroid out of orbit.


Watch The Skies

So the news isn’t that great. If we spot one, we have a while to plan, but if we don’t, we are doomed. But don’t lose hope, the chances of being hit by something big enough to wipe us out are low, and technology is improving every day. Asteroids are just another evolutionary pressure, and at some point any spacefaring civilisation will have to learn to deal with them.

We have done well so far.

What’s Next?

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The opinions expressed in this article are those of Dr Janaway alone and may not represent those of his affiliates. Images courtesy of NASA Goddard Space Flight.


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