The most devastating extinctions, when almost the entire life on earth was wiped out, had happened in prehistoric times. The most recent was 66 million years ago when dinosaurs were killed off.

Though scientists are still not agreed on what caused these mass extinctions - global warming or oxygen depletion in seas or meteor hits or massive methane leaks from ocean ice or COVID-like epidemics or hell-hot hurricanes called hypercanes - there is a general consensus that the dinosaur-ending disaster, called the Cretaceous Event, was caused by an asteroid hit.

Acid attack
It is said that a giant asteroid some 15 km wide had dropped on the Earth obliterating nearly 70 per cent of the Earth's species including dinosaurs. It is not as if right on impact a 15-km wide asteroid crushed the entire life on earth with a circumference of over 40,000 kilometres.

It was the chemical reactions set off by the asteroid hit that did the damage. The giant interstellar stone bombed the sulphur-rich rock bottom of a shallow sea at a certain angle causing a massive upsurge of liquid sulphur. The sulphur rose into an atmosphere that, unlike today, had highly combustible oxygen.

For months the earth was soaked in acidic rains powerful enough to bore through dinosaur skins, melt their innards and crumple them into burnt limp skin sacks.

But despite scientific evidence, dinosaur extinction is too fantastic an event that seems more likely to have happened in the hyper-imagined worlds of our mighty epics than in reality.

Poor man's asteroid attack
In comparison, the largest asteroid event in recorded history could seem as tame as a mango falling on a roof. It occurred relatively recently, on June 30, 1908, near the Podkamennaya Tunguska River in Eastern Siberia, Russia.

If the asteroid that killed dinosaurs was 15 kilometres wide, the Tunguska one was 60 metres, just about the width of Kerala's Secretariat. It had flattened 2150 square kilometres of forest, far less than the 3728 sq km of Nagarjunsagar-Srisailam Tiger Reserve, the biggest in India.

Since the asteroid dropped over a largely uninhabited area, human casualties were virtually nil.

The latest meteor strike on earth was also recorded in Russia, at Chelyabinsk on February 15, 2013. This was a meteor 20 metres wide and exploded before impact. The meteor dust flew nearly 25 km. Since it was a town, nearly 8000 buildings were damaged and hundreds suffered non-fatal injuries from the destruction that the asteroid explosion set off.

Small but dodgy stones
If the Tunguska event is considered a major impactor, the Chelyabinsk is a minor one. “Luckily, the big impactors happen less frequently than the small ones,” said Kerala-educated Aswin Sekhar, India's first professional meteor scientist. Sekhar is also an affiliate of the prestigious Institute of Celestial Mechanics and Calculation of Ephemeris, France.

“If a Tunguska-like event occurs every 100 years, a minor Chelyabinsk-like event happens every 10 years,” Sekhar said. He was in the capital city to deliver the Krishna Warrier Lecture organised as part of the 13th anniversary of Amateur Astronomers' Organisation (AASTRO) Kerala.

The problem with smaller asteroids is that they are elusive. “We do have a very good approximation and idea about all the asteroids above one kilometre in size,” Sekhar told Onmanorama on Sunday.

“When it comes to smaller asteroids, we don't really have a complete mapping or we don't exactly know where they are. This in effect would mean that we could always have an unexpected asteroid visiting us at some point without much warning. That I think is the biggest risk to Earth,” the young theoretical astrophysicist said.

Apocalypse now
There are, of course, multiple new tracking programmes and survey telescopes trying to map as many asteroids as possible.

This was how the Apophis (Asteroid 99942) threat was detected by astronomers. It was nearly 350 metres and, when it was first spotted in 2004, was considered the most dangerous asteroid that could hit Earth. Then, it was said Apophid could come terribly close by 2029.

“Apophis was a surprising sort of threat in the sense that, at some point during the initial observations, its probability of impact on earth came to 3 percent, which is extremely high for the impact calculations. But later observation and better approximations to orbit reduced the probability and now it is in a safe spot,” Sekhar said.

According to NASA, there is a slight 0.006 per cent chance of Apophis hitting Earth in 2068. Almost all the 24 asteroids listed in the Sentry Impact List Table of NASA's Center for Near-Earth Object Studies (CNEOS) have a less than one per cent chance of bumping into the Earth.

The highest probability is for a small asteroid christened 2010 RF12. This one with a diameter of 0.007 has a 10 per cent chance of ramming into the Earth between 2095 and 2122; a possible date given is September 5, 2095.

Be warned or be doomed
For every potentially damaging asteroid spotted, there are millions falling towards the Earth unseen.

“We still don't have a complete holistic picture yet. Which actually means that there are still a lot of objects undiscovered and some of these objects can come close to earth any time and we don't know whether any of them have a trajectory that can collide with the earth,” Sekhar said.

“If we get sufficient warning, we have good ways to understand its orbit better and what we need is more and more observations so that we can try to understand how the trajectory evolves over time,” he said.

Asteroid-proof Earth
However, it is not just enough to spot these killer asteroids. The world should also be able to throw a protective armour around it.

“Risk mitigation is still at an infant stage. There are plenty of new missions and projects coming up trying to understand with new strategies as to how to ward off some of these threats, how to give a nudge to some of these asteroids and change its trajectory so that it misses our earth rather than collide with it. But these are all works in progress,” he said.

Armageddon plan revised
The most promising he said was the DART (Double Asteroid Redirection Test) Mission of NASA.

DART Mission's objective is to push a potentially-dangerous asteroid off its path. It's a sort of suicide mission where the DART spacecraft deliberately rams into the target asteroid and force it to change course.

In fact, DART is a safer and refined version of the 'Armageddon' plan. In the 1998 Michael Bay movie starring Bruce Willis, astronauts drill a hole into the rogue asteroid to insert a nuclear bomb into it.

Last October, NASA put out a press statement saying that DART spacecraft collision with a target asteroid did indeed alter its orbit.

“This marks humanity’s first time purposely changing the motion of a celestial object and the first full-scale demonstration of asteroid deflection technology,” NASA said in a statement on October 11, 2022.

This offers hope that, if at all Apophid hurls itself terribly close to Earth in 2068, it could be easily glanced off its dangerous trajectory.