Asteroids are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago. The current known asteroid count is 1,309,406.
It happened some 66 million years ago. That is really a long time ago, considering that humans’ ape-like ancestors are believed to have appeared only five to seven million years ago. Dinosaurs had been ruling the roost on the planet Earth for about 245 million years and must have gotten used to their ‘boring’ life of hunting or chomping vegetation. Then ‘the thing’ happened. Some of them could see a white flash of light in the northeastern sky even during the daytime. It quickly grew larger and larger, accompanied by a menacing thunder and then the ground under their massive feet shook uncontrollably with the sound of a terrible explosion. That was the last thing they would remember.
Asteroid impact and extinction of Dinosaurs
On that fateful day, an asteroid some 10-15 km wide, moving at a fearsome speed of 20 km per second struck the shallow sea in what is now Yucatan Peninsula in the Gulf of Mexico. You can get an idea of the speed of the asteroid by comparing it with the fastest man-made object. It is the New Horizons space probe launched in 2006 by an Atlas V rocket that achieved a speed of 16.26 km per second. But, it weighed just 478 kg. That asteroid weighed nearly a thousand billion tons. Asteroids are the rocky remnants of material leftover from the formation of the solar system. Most of them are found in the ‘asteroid belt’ located between Mars and Jupiter. There are between 1.1 and 1.9 million asteroids larger than 1 kilometre in size, and millions of smaller ones. The massive gravitational pull of Jupiter can hurl them in random directions hence the danger.
The impact of that dinosaur-era asteroid produced energy equivalent to about 100 trillion tons of TNT (that is, about 6 billion Hiroshima-type bombs exploded simultaneously). It left a transient cavity some 100 km wide and 30 km deep. It later collapsed leaving a crater some 180 km wide and 20 km deep, now covered by thousands of feet of sediment. It lies close to the current towns of Chicxulub Pueblo and Chicxulub Puerto and is known as the Chicxulub Crater.
The heat produced by the impact destroyed and vaporized the asteroid completely. As a result, a massive plume of some 25 trillion tons of vapour and molten debris shot up and even beyond the atmosphere into space. Eventually, most of it rained down over North America, incinerating everything within a radius of more than 1,600 km and causing wildfires in 70% of the world’s forests. Superheated winds moving over 1,000 kmph radiated 900 to 1,800 km out from the impact point, destroying vegetation and killing animals. The impact produced earthquakes of magnitude 9 to 11 on the Richter scale that triggered earthquakes and volcanic activity around the world. The impact produced a mile-high mega-tsunami and subsequent global tsunamis 50 to 150 m high produced by earthquakes causing widespread destruction.
The debris and soot thrown up in the atmosphere around the world produced a nuclear-winter-like effect by blocking the sun. Decades later, the greenhouse effect led to global warming that melted the polar ice caps. The resulting global climate disruptions led to the extinction of nearly 70% of the animal species on the planet including the mighty non-avian dinosaurs as well as plants that could not adapt to the changes. It is known as the K-T Extinction.
You will be amused to learn that this hypothesis was developed as late as 1980 only by the Nobel Laureate nuclear physicist Luis Walter Alvarez and his geologist son who found that there is an unusually high amount of Iridium in the sedimentary rocks. Alvarez had earlier worked on the Manhattan Project during the Second World War and had developed the Exploding Bridge-Wire Detonators for the Nagasaki atom bomb. Iridium is rare in the Earth’s crust but is much more abundant in asteroids. Detailed experimental confirmation of their hypothesis came later through the work of the JOIDES Resolution (a giant drilling ship), a lift boat called Myrtle, and the International Ocean Discovery Project.
It could happen to us too
The point to be noted is that a meteor, a thousand times smaller in length than our planet, killed nearly three-fourths of life on Earth even as it had animals sturdier than humans and who were not as densely populated as humans. It is like a bullet just seven hundredth of an inch in calibre, killing a six-foot man! An asteroid strike of the same size as K-T Extinction would be an extinction-level event for us with few survivors. An asteroid of 96 km in size would mean 100% extinction. Even much smaller asteroids could kill billions depending on where they strike due to earthquakes, tsunamis and unbearable climate disruptions. An asteroid half a mile wide would, on impact, produce energy equal to six million Hiroshima bombs exploded together. For that matter, even an asteroid the size of a small house hitting a city will pulverize everything in a radius of half a mile from the point of impact and damage structures way beyond too.
The earth absorbs 5 to 300 tons of extra-terrestrial material from about 25 million meteoroids every day. Usually, they are very small and burn up in the atmosphere resulting in the familiar shooting stars or meteors. Very few of them reach Earth and become meteorites. But, you never know when a big boy could be thrown our way. The next time a mile-wide asteroid passes close to Earth will be on October 26, 2028—but is expected to pass harmlessly. It will be about two and a half times the Moon’s distance from Earth at its closest point.
Moreover if, by any chance, the asteroid happens to come from a retrograde orbit, that is, moving in opposite direction than the earth, it could impact with a maximum velocity touching 73.6 km per second! The most probable trajectory is a 45-degree impact, affording you a full and terrifying view of the incoming disaster.
Also Read: Space debris: is the USA serious about solving the problem?
To date, only about 40 per cent of 460-foot-plus (140-meter-plus) sized asteroids have been found. Any object bigger than a kilometre hitting the earth will have global catastrophic ramifications. That means it makes sense to be prepared for such an event. Obviously, we cannot let ourselves be destroyed by a lifeless visitor from outer space—we must be prepared for the defence of our planet.
How to deflect or destroy asteroids?
Several techniques have been worked out.
Kinetic impactor: This is presently the most favoured technique. The basic idea involves college physics. Slam the asteroid with a spacecraft in kamikaze mode. Though the spacecraft is tiny in comparison and it would do little to destroy the asteroid, the impact would change the asteroid’s trajectory, however slightly. Still, because the asteroid is millions of miles away from the earth, the slight nudge also would enable it to sail harmlessly away from us by the time it comes close.
The Kinetic Impactor has been tested on an actual asteroid. In 2022, the DART (NASA’s Double Asteroid Redirection Test), a nine feet craft of just 610 kg intentionally crashed into the 177-meter wide and 5 million tons heavy asteroid Dimorphos at a speed of 6.1 km per second after travelling for over 10 months. Dimorphos actually orbits around another asteroid Didymos. There was a reason to choose it. It was observed after the impact that Dimorphos’ orbit changed by 33 minutes, confirming that the nudge actually deflected it successfully.
Gravity tractor: A gravity tractor would be a spacecraft that would fly alongside an asteroid, using its gravitational pull to tug on the asteroid and slowly change its trajectory. You have to start it with a lead time of years. The pull would be too small for asteroids bigger than half a km. However, the technique would keep us in control all the time.
Laser ablation: Contrary to what sci-fi buffs might think, this is not intended to destroy the asteroid. We don’t have those powerful lasers nor are likely to have them. The laser will vaporize a part of the asteroid where it is focused. The hot vaporized material will fly away from the asteroid. In that process, by Newton’s Third Law of Motion, it will apply a thrust on the asteroid; in much the same way air escaping from a balloon makes it move. In principle, it is like the famous Radiation Implosion technique used on hydrogen bombs.
Ion beam shepherd: This technique envisages that a spacecraft would be sent close to the asteroid and its ion engine (an engine that, instead of hot gases produced by burning of propellant, uses ions that are electrically charged atoms moving at extremely high velocities for propulsion) exhaust would gently push the asteroid gradually over months or years. Ion engines can work for very long periods whereas chemical propellants burn out in a matter of minutes.
Nuclear blast: This is the manliest of all techniques. Many of you must have seen the Hollywood super-hit film Armageddon (1998) starring Bruce Willis. A massive asteroid the size of Texas is hurtling towards Earth. NASA devised a plan to have a deep hole drilled into the asteroid, into which they would insert and detonate a nuclear bomb to destroy the asteroid. Two Space Shuttles are launched and despite accidents, they manage to drill the hole to the required depth. However, their remote detonator is damaged and someone must stay behind to detonate it manually. In a manner quintessentially heroic, so typical of Hollywood, Willis sacrifices his life to detonate the device and save the planet.
Very exciting and heroic to blow the devil up but, in practice, drilling a hole to a certain depth in an asteroid is fraught with too many risks and uncertainties. You detonate at less than the required depth in a hurry and you will get not one but several smaller pieces of the asteroid impacting the earth in a meteor shower, causing more widespread damage. Still, if the asteroid is small (say 100 meters wide) and you explode a nuke next to it when it is two months away from impact, it would despatch 99.9% of the material away from Earth. We could think of it as the last-ditch defence when everything else fails.
Apparently, taking a cue from this, there are conspiracy theories (notably by Russian nationalist leader Vladimir Zhirinovsky, though officially countered by the Russian Emergency Ministry) that the meteor shower over the city of Chelyabinsk, in west-central Russia, close to the Ural Mountains on February 15, 2013, was the result of a meteor breaking up in the atmosphere because the Americans tested some new weapon on it. American conspiracy theorist Alex Jones, who runs the website Infowars, supported it and added that the US had even given advance notice to Russia. In any case, nobody is aware of any new or wonder weapon, and nobody detected any nuclear explosion in the atmosphere.
Trust the planetary defence force
As a scientist I am convinced that we would be able to save the world from an asteroid strike by one or more of these techniques provided we detect them early. Like cancer, here also the key to survival lies in detecting them early enough. This is what NASA’s Planetary Defense Coordination Office does—keeping a watchful eye on the movement of all Near Earth Objects (NEOs). A NEO is anything, asteroid, comet or whatever, that comes near 45 million km of the earth. NASA’s Jet Propulsion Laboratory’s CNEOS (Center for NEOs) tracks their orbits carefully and makes projections for the future.
Take my advice; do not waste your hard-earned money on some weird insurance policy even if they sell one. If these techniques do not work, nobody will be left to pay the insured amount or make use of it!
