26th April 2025
One of my favourite movies is Armageddon with Bruce Willis. It has the perfect mix of schmaltz, drama, rousing speeches and giggles. I didn’t say it was Oscar winning but I defy you to say you couldn’t watch it again and again and…..
The central theme of a killer rock from outer space only just foiled by human ingenuity, was perfect fodder for a brain simmered from young on the thought of asteroids presaging catastrophe being commonplace. That the chances of the Earth being thwacked with devastating consequences was…well high. An asteroid struck Earth 66million years ago and wiped out c80% of the plant and animal species including non-avian dinosaurs. The Nasa asteroid impact exercise of April 2023 suggested a 300m wide asteroid could release energy equivalent to 133,000 times of the bomb which destroyed Hiroshima at the end of World War II. At three times the size (which doesn’t seem particularly large in the vastness of space terms), an asteroid is deemed a ‘Planet killer’. So it is understandable my flustered mind could not comprehend why others were not ruminating on this foreboding wisdom as I had been?
Perhaps to reduce my heart rate, it’s best to build up some knowledge – clearly more for me than for you. Much of the below is gleaned from Nasa, The BBC and other science websites.
Asteroids are small rocky objects which orbit the sun forming when our universe did – in the Big Bang c4.6bn years ago. Gas, dust and other minerals collapsed to forge the sun, planets, stars. The leftover lumps or rubble loosely held together are what we today call asteroids. No two are thought to be alike. Tending to be of irregular shape, pitted, airless, rotating, possessing various compositions of rocks and minerals, with some having companion moons. Most asteroids are smaller than planets but size varies from inconsequential at 10m across to the largest thought to be 530km in diameter. Within our solar system hundreds of thousands to possibly millions of asteroids exist with the majority thought to reside in the donut shaped asteroid belt circumnavigating the sun. This is a part of space we have located between the orbits of Mars and Jupiter.
Some further clarifications if like me you use these following words interchangeably. A meteoroid is a fragment of an asteroid, comet, planet, moon – varying from an asteroid by bulk as these are usually pebble sized. Whatever hits the topside of Earth and remains is called a meteorite. The bright burning trail of a meteoroid in our atmosphere (essentially burning rocks) is termed a meteor or more colloquially shooting stars. A comet is also a remnant from the big bang circuiting the sun. However it is composed of ice and dust which if within particular distance of the sun, melts into a Coma revealing two bright tails of dust and gas. Nasa suggest billions of comets occupy our solar system.
Not all asteroids settle in the asteroid belt. We have observed these, along with asteroids inhabiting the belt, being nudged by the gravity of other bodies in the solar system into our orbit (within 48 million kms of the Earth). Anything within this orbit is known as a Near Earth Object – a NEO. c99% of our NEOs are asteroids. The European Space Agency approximates c20,000 are notable but I have read of estimates double that. This vagueness is forgivable; asteroids due to their constitution, lack of light reflection in addition to the obfuscation of the Earth’s atmosphere are not easy to track. We look to follow NEOs using telescopes and radar on Earth and in space, employing automated collision systems aiming to predict where they are headed and the likelihood of damage to the Earth over the next 100 years. But let us be clear – our figures are not accurate and we haven’t found all of these NEOs let alone able to track their paths.
If an asteroid has the potential to make an ominously close approach to Earth it is called a ‘Potentially Hazardous Object’ and is monitored closely. This Nasa website shows the asteroids Nasa tracks in neat graphics. https://eyes.nasa.gov/apps/asteroids/#/home Around 1,700 of these asteroids are thought to have a collision risk with Earth and at any time the newspapers will nervously highlight one menacing asteroid which has turned its gaze towards Earth.
Let us return to my irrationality. According to the BBC website, each year we are bombarded with 5,200 tonnes of space dust and once a year an asteroid the size of a car enters our atmosphere and before reaching our surface is incinerated. This is additional to man made space debris (e.g used up satellites) where an average of one piece a day has been known to hit our ground. On the face of it this sounds high but in practical terms making assumptions around burn, population density and spread, it apparently translates into 1 death every 1,300 years.
Size, composition, angle and speed all influence the impact of any asteroid but in crude terms the likelihood of a planet killer taking aim at us Nasa estimate at occurring once every 700,000 years and a Continent killer every 70,000 years. The type of asteroid that killed the Dinosaurs was 10km across and scientists put a probability on another hitting the Earth as once in 30 million years. I guess the key question is what distribution model is being employed and what’s the start date because I’ve seen alot of variation in those figures!
But let’s assume one was on track to hit Earth, what could be done? Only if we become aware of such an object years in advance could a deflection mission be put into action. You find Bruce Willis and…only joking. If we were to apply a nuclear bomb as in the movie, the debris could be just as damaging to Earth and recent research indicates due to gravity the asteroid may re-form continuing on its destructive route. However we could use nuclear bombs to deflect an asteroid from its path. Some have suggested mounted thrusters or solar flares utilising energy from the sun to do the same. New ideas are being developed all the time but most require having years to plan and execute and in truth are highly theoretical. If a NEO was to shift path quickly I’m unsure what the options are other than to sit comfortably with some popcorn and jokes aside, really hope Nasa are calling Bruce…..
Curiosity and the rascal 